Implement P1209 - Adopt Consistent Container Erasure from Library Fundamentals 2 for C++20. Reviewed as https://reviews.llvm.org/D55532

27 files changed, 1531 insertions, 0 deletions

diff --git a/libcxx/test/std/containers/associative/map/map.erasure/erase_if.pass.cpp b/libcxx/test/std/containers/associative/map/map.erasure/erase_if.pass.cpp
new file mode 100644
index 00000000000..f8cbc15d164
--- /dev/null
+++ b/libcxx/test/std/containers/associative/map/map.erasure/erase_if.pass.cpp
@@ -0,0 +1,79 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <map>
+
+// template <class Key, class T, class Compare, class Allocator, class Predicate>
+//   void erase_if(map<Key, T, Compare, Allocator>& c, Predicate pred);
+
+#include <map>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+using Init = std::initializer_list<int>;
+template <typename M>
+M make (Init vals)
+{
+    M ret;
+    for (int v : vals)
+        ret[v] = v + 10;
+    return ret;
+}
+
+template <typename M, typename Pred>
+void
+test0(Init vals, Pred p, Init expected)
+{
+    M s = make<M> (vals);
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    assert(s == make<M>(expected));
+}
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v.first == 1;};
+    auto is2 = [](auto v) { return v.first == 2;};
+    auto is3 = [](auto v) { return v.first == 3;};
+    auto is4 = [](auto v) { return v.first == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0<S>({}, is1, {});
+
+    test0<S>({1}, is1, {});
+    test0<S>({1}, is2, {1});
+
+    test0<S>({1,2}, is1, {2});
+    test0<S>({1,2}, is2, {1});
+    test0<S>({1,2}, is3, {1,2});
+
+    test0<S>({1,2,3}, is1, {2,3});
+    test0<S>({1,2,3}, is2, {1,3});
+    test0<S>({1,2,3}, is3, {1,2});
+    test0<S>({1,2,3}, is4, {1,2,3});
+
+    test0<S>({1,2,3}, True,  {});
+    test0<S>({1,2,3}, False, {1,2,3});
+}
+
+int main()
+{
+    test<std::map<int, int>>();
+    test<std::map<int, int, std::less<int>, min_allocator<std::pair<const int, int>>>> ();
+    test<std::map<int, int, std::less<int>, test_allocator<std::pair<const int, int>>>> ();
+
+    test<std::map<long, short>>();
+    test<std::map<short, double>>();
+}
+
diff --git a/libcxx/test/std/containers/associative/multimap/multimap.erasure/erase_if.pass.cpp b/libcxx/test/std/containers/associative/multimap/multimap.erasure/erase_if.pass.cpp
new file mode 100644
index 00000000000..8e786fdc947
--- /dev/null
+++ b/libcxx/test/std/containers/associative/multimap/multimap.erasure/erase_if.pass.cpp
@@ -0,0 +1,89 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <map>
+
+//   template <class Key, class T, class Compare, class Allocator, class Predicate>
+//     void erase_if(multimap<Key, T, Compare, Allocator>& c, Predicate pred);
+
+#include <map>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+using Init = std::initializer_list<int>;
+template <typename M>
+M make (Init vals)
+{
+    M ret;
+    for (int v : vals)
+        ret.insert(typename M::value_type(v, v + 10));
+    return ret;
+}
+
+template <typename M, typename Pred>
+void
+test0(Init vals, Pred p, Init expected)
+{
+    M s = make<M> (vals);
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    assert(s == make<M>(expected));
+}
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v.first == 1;};
+    auto is2 = [](auto v) { return v.first == 2;};
+    auto is3 = [](auto v) { return v.first == 3;};
+    auto is4 = [](auto v) { return v.first == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0<S>({}, is1, {});
+
+    test0<S>({1}, is1, {});
+    test0<S>({1}, is2, {1});
+
+    test0<S>({1,2}, is1, {2});
+    test0<S>({1,2}, is2, {1});
+    test0<S>({1,2}, is3, {1,2});
+    test0<S>({1,1}, is1, {});
+    test0<S>({1,1}, is3, {1,1});
+
+    test0<S>({1,2,3}, is1, {2,3});
+    test0<S>({1,2,3}, is2, {1,3});
+    test0<S>({1,2,3}, is3, {1,2});
+    test0<S>({1,2,3}, is4, {1,2,3});
+
+    test0<S>({1,1,1}, is1, {});
+    test0<S>({1,1,1}, is2, {1,1,1});
+    test0<S>({1,1,2}, is1, {2});
+    test0<S>({1,1,2}, is2, {1,1});
+    test0<S>({1,1,2}, is3, {1,1,2});
+    test0<S>({1,2,2}, is1, {2,2});
+    test0<S>({1,2,2}, is2, {1});
+    test0<S>({1,2,2}, is3, {1,2,2});
+    
+    test0<S>({1,2,3}, True,  {});
+    test0<S>({1,2,3}, False, {1,2,3});
+}
+
+int main()
+{
+    test<std::multimap<int, int>>();
+    test<std::multimap<int, int, std::less<int>, min_allocator<std::pair<const int, int>>>> ();
+    test<std::multimap<int, int, std::less<int>, test_allocator<std::pair<const int, int>>>> ();
+
+    test<std::multimap<long, short>>();
+    test<std::multimap<short, double>>();
+}
diff --git a/libcxx/test/std/containers/associative/multiset/multiset.erasure/erase_if.pass.cpp b/libcxx/test/std/containers/associative/multiset/multiset.erasure/erase_if.pass.cpp
new file mode 100644
index 00000000000..3c619bb687f
--- /dev/null
+++ b/libcxx/test/std/containers/associative/multiset/multiset.erasure/erase_if.pass.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <set>
+
+// template <class T, class Compare, class Allocator, class Predicate>
+//   void erase_if(multiset<T, Compare, Allocator>& c, Predicate pred);
+
+#include <set>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class Pred>
+void
+test0(S s, Pred p, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    assert(s == expected);
+}
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v == 1;};
+    auto is2 = [](auto v) { return v == 2;};
+    auto is3 = [](auto v) { return v == 3;};
+    auto is4 = [](auto v) { return v == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0(S(), is1, S());
+
+    test0(S({1}), is1, S());
+    test0(S({1}), is2, S({1}));
+
+    test0(S({1,2}), is1, S({2}));
+    test0(S({1,2}), is2, S({1}));
+    test0(S({1,2}), is3, S({1,2}));
+    test0(S({1,1}), is1, S());
+    test0(S({1,1}), is3, S({1,1}));
+
+    test0(S({1,2,3}), is1, S({2,3}));
+    test0(S({1,2,3}), is2, S({1,3}));
+    test0(S({1,2,3}), is3, S({1,2}));
+    test0(S({1,2,3}), is4, S({1,2,3}));
+
+    test0(S({1,1,1}), is1, S());
+    test0(S({1,1,1}), is2, S({1,1,1}));
+    test0(S({1,1,2}), is1, S({2}));
+    test0(S({1,1,2}), is2, S({1,1}));
+    test0(S({1,1,2}), is3, S({1,1,2}));
+    test0(S({1,2,2}), is1, S({2,2}));
+    test0(S({1,2,2}), is2, S({1}));
+    test0(S({1,2,2}), is3, S({1,2,2}));
+    
+    test0(S({1,2,3}), True,  S());
+    test0(S({1,2,3}), False, S({1,2,3}));
+}
+
+int main()
+{
+    test<std::multiset<int>>();
+    test<std::multiset<int, std::less<int>, min_allocator<int>>> ();
+    test<std::multiset<int, std::less<int>, test_allocator<int>>> ();
+
+    test<std::multiset<long>>();
+    test<std::multiset<double>>();
+}
diff --git a/libcxx/test/std/containers/associative/set/set.erasure/erase_if.pass.cpp b/libcxx/test/std/containers/associative/set/set.erasure/erase_if.pass.cpp
new file mode 100644
index 00000000000..a55a38c2d56
--- /dev/null
+++ b/libcxx/test/std/containers/associative/set/set.erasure/erase_if.pass.cpp
@@ -0,0 +1,67 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <set>
+
+// template <class T, class Compare, class Allocator, class Predicate>
+//   void erase_if(set<T, Compare, Allocator>& c, Predicate pred);
+
+#include <set>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class Pred>
+void
+test0(S s, Pred p, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    assert(s == expected);
+}
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v == 1;};
+    auto is2 = [](auto v) { return v == 2;};
+    auto is3 = [](auto v) { return v == 3;};
+    auto is4 = [](auto v) { return v == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0(S(), is1, S());
+
+    test0(S({1}), is1, S());
+    test0(S({1}), is2, S({1}));
+
+    test0(S({1,2}), is1, S({2}));
+    test0(S({1,2}), is2, S({1}));
+    test0(S({1,2}), is3, S({1,2}));
+
+    test0(S({1,2,3}), is1, S({2,3}));
+    test0(S({1,2,3}), is2, S({1,3}));
+    test0(S({1,2,3}), is3, S({1,2}));
+    test0(S({1,2,3}), is4, S({1,2,3}));
+
+    test0(S({1,2,3}), True,  S());
+    test0(S({1,2,3}), False, S({1,2,3}));
+}
+
+int main()
+{
+    test<std::set<int>>();
+    test<std::set<int, std::less<int>, min_allocator<int>>> ();
+    test<std::set<int, std::less<int>, test_allocator<int>>> ();
+
+    test<std::set<long>>();
+    test<std::set<double>>();
+}
diff --git a/libcxx/test/std/containers/sequences/deque/deque.erasure/erase.pass.cpp b/libcxx/test/std/containers/sequences/deque/deque.erasure/erase.pass.cpp
new file mode 100644
index 00000000000..9a8c698a5ff
--- /dev/null
+++ b/libcxx/test/std/containers/sequences/deque/deque.erasure/erase.pass.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <deque>
+
+// template <class T, class Allocator, class U>
+//   void erase(deque<T, Allocator>& c, const U& value);
+  
+
+#include <deque>
+#include <optional>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class U>
+void
+test0(S s,  U val, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase(s, val)));
+    std::erase(s, val);
+    assert(s == expected);
+}
+
+template <class S>
+void test()
+{
+
+    test0(S(), 1, S());
+
+    test0(S({1}), 1, S());
+    test0(S({1}), 2, S({1}));
+
+    test0(S({1,2}), 1, S({2}));
+    test0(S({1,2}), 2, S({1}));
+    test0(S({1,2}), 3, S({1,2}));
+    test0(S({1,1}), 1, S());
+    test0(S({1,1}), 3, S({1,1}));
+
+    test0(S({1,2,3}), 1, S({2,3}));
+    test0(S({1,2,3}), 2, S({1,3}));
+    test0(S({1,2,3}), 3, S({1,2}));
+    test0(S({1,2,3}), 4, S({1,2,3}));
+
+    test0(S({1,1,1}), 1, S());
+    test0(S({1,1,1}), 2, S({1,1,1}));
+    test0(S({1,1,2}), 1, S({2}));
+    test0(S({1,1,2}), 2, S({1,1}));
+    test0(S({1,1,2}), 3, S({1,1,2}));
+    test0(S({1,2,2}), 1, S({2,2}));
+    test0(S({1,2,2}), 2, S({1}));
+    test0(S({1,2,2}), 3, S({1,2,2}));
+
+//  Test cross-type erasure
+    using opt = std::optional<typename S::value_type>;
+    test0(S({1,2,1}), opt(),  S({1,2,1}));
+    test0(S({1,2,1}), opt(1), S({2}));
+    test0(S({1,2,1}), opt(2), S({1,1}));
+    test0(S({1,2,1}), opt(3), S({1,2,1}));
+}
+
+int main()
+{
+    test<std::deque<int>>();
+    test<std::deque<int, min_allocator<int>>> ();
+    test<std::deque<int, test_allocator<int>>> ();
+
+    test<std::deque<long>>();
+    test<std::deque<double>>();
+}
diff --git a/libcxx/test/std/containers/sequences/deque/deque.erasure/erase_if.pass.cpp b/libcxx/test/std/containers/sequences/deque/deque.erasure/erase_if.pass.cpp
new file mode 100644
index 00000000000..a090eb6947d
--- /dev/null
+++ b/libcxx/test/std/containers/sequences/deque/deque.erasure/erase_if.pass.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <deque>
+
+// template <class T, class Allocator, class Predicate>
+//   void erase_if(deque<T, Allocator>& c, Predicate pred);  
+
+#include <deque>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class Pred>
+void
+test0(S s, Pred p, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    assert(s == expected);
+}
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v == 1;};
+    auto is2 = [](auto v) { return v == 2;};
+    auto is3 = [](auto v) { return v == 3;};
+    auto is4 = [](auto v) { return v == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0(S(), is1, S());
+
+    test0(S({1}), is1, S());
+    test0(S({1}), is2, S({1}));
+
+    test0(S({1,2}), is1, S({2}));
+    test0(S({1,2}), is2, S({1}));
+    test0(S({1,2}), is3, S({1,2}));
+    test0(S({1,1}), is1, S());
+    test0(S({1,1}), is3, S({1,1}));
+
+    test0(S({1,2,3}), is1, S({2,3}));
+    test0(S({1,2,3}), is2, S({1,3}));
+    test0(S({1,2,3}), is3, S({1,2}));
+    test0(S({1,2,3}), is4, S({1,2,3}));
+
+    test0(S({1,1,1}), is1, S());
+    test0(S({1,1,1}), is2, S({1,1,1}));
+    test0(S({1,1,2}), is1, S({2}));
+    test0(S({1,1,2}), is2, S({1,1}));
+    test0(S({1,1,2}), is3, S({1,1,2}));
+    test0(S({1,2,2}), is1, S({2,2}));
+    test0(S({1,2,2}), is2, S({1}));
+    test0(S({1,2,2}), is3, S({1,2,2}));
+    
+    test0(S({1,2,3}), True,  S());
+    test0(S({1,2,3}), False, S({1,2,3}));
+}
+
+int main()
+{
+    test<std::deque<int>>();
+    test<std::deque<int, min_allocator<int>>> ();
+    test<std::deque<int, test_allocator<int>>> ();
+
+    test<std::deque<long>>();
+    test<std::deque<double>>();
+}
diff --git a/libcxx/test/std/containers/sequences/forwardlist/forwardlist.erasure/erase.pass.cpp b/libcxx/test/std/containers/sequences/forwardlist/forwardlist.erasure/erase.pass.cpp
new file mode 100644
index 00000000000..0163b8607cb
--- /dev/null
+++ b/libcxx/test/std/containers/sequences/forwardlist/forwardlist.erasure/erase.pass.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <forward_list>
+
+// template <class T, class Allocator, class U>
+//   void erase(forward_list<T, Allocator>& c, const U& value);
+  
+
+#include <forward_list>
+#include <optional>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class U>
+void
+test0(S s,  U val, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase(s, val)));
+    std::erase(s, val);
+    assert(s == expected);
+}
+
+template <class S>
+void test()
+{
+
+    test0(S(), 1, S());
+
+    test0(S({1}), 1, S());
+    test0(S({1}), 2, S({1}));
+
+    test0(S({1,2}), 1, S({2}));
+    test0(S({1,2}), 2, S({1}));
+    test0(S({1,2}), 3, S({1,2}));
+    test0(S({1,1}), 1, S());
+    test0(S({1,1}), 3, S({1,1}));
+
+    test0(S({1,2,3}), 1, S({2,3}));
+    test0(S({1,2,3}), 2, S({1,3}));
+    test0(S({1,2,3}), 3, S({1,2}));
+    test0(S({1,2,3}), 4, S({1,2,3}));
+
+    test0(S({1,1,1}), 1, S());
+    test0(S({1,1,1}), 2, S({1,1,1}));
+    test0(S({1,1,2}), 1, S({2}));
+    test0(S({1,1,2}), 2, S({1,1}));
+    test0(S({1,1,2}), 3, S({1,1,2}));
+    test0(S({1,2,2}), 1, S({2,2}));
+    test0(S({1,2,2}), 2, S({1}));
+    test0(S({1,2,2}), 3, S({1,2,2}));
+
+//  Test cross-type erasure
+    using opt = std::optional<typename S::value_type>;
+    test0(S({1,2,1}), opt(),  S({1,2,1}));
+    test0(S({1,2,1}), opt(1), S({2}));
+    test0(S({1,2,1}), opt(2), S({1,1}));
+    test0(S({1,2,1}), opt(3), S({1,2,1}));
+}
+
+int main()
+{
+    test<std::forward_list<int>>();
+    test<std::forward_list<int, min_allocator<int>>> ();
+    test<std::forward_list<int, test_allocator<int>>> ();
+
+    test<std::forward_list<long>>();
+    test<std::forward_list<double>>();
+}
diff --git a/libcxx/test/std/containers/sequences/forwardlist/forwardlist.erasure/erase_if.pass.cpp b/libcxx/test/std/containers/sequences/forwardlist/forwardlist.erasure/erase_if.pass.cpp
new file mode 100644
index 00000000000..69685d2d35f
--- /dev/null
+++ b/libcxx/test/std/containers/sequences/forwardlist/forwardlist.erasure/erase_if.pass.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <forward_list>
+
+// template <class T, class Allocator, class Predicate>
+//   void erase_if(forward_list<T, Allocator>& c, Predicate pred);  
+
+#include <forward_list>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class Pred>
+void
+test0(S s, Pred p, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    assert(s == expected);
+}
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v == 1;};
+    auto is2 = [](auto v) { return v == 2;};
+    auto is3 = [](auto v) { return v == 3;};
+    auto is4 = [](auto v) { return v == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0(S(), is1, S());
+
+    test0(S({1}), is1, S());
+    test0(S({1}), is2, S({1}));
+
+    test0(S({1,2}), is1, S({2}));
+    test0(S({1,2}), is2, S({1}));
+    test0(S({1,2}), is3, S({1,2}));
+    test0(S({1,1}), is1, S());
+    test0(S({1,1}), is3, S({1,1}));
+
+    test0(S({1,2,3}), is1, S({2,3}));
+    test0(S({1,2,3}), is2, S({1,3}));
+    test0(S({1,2,3}), is3, S({1,2}));
+    test0(S({1,2,3}), is4, S({1,2,3}));
+
+    test0(S({1,1,1}), is1, S());
+    test0(S({1,1,1}), is2, S({1,1,1}));
+    test0(S({1,1,2}), is1, S({2}));
+    test0(S({1,1,2}), is2, S({1,1}));
+    test0(S({1,1,2}), is3, S({1,1,2}));
+    test0(S({1,2,2}), is1, S({2,2}));
+    test0(S({1,2,2}), is2, S({1}));
+    test0(S({1,2,2}), is3, S({1,2,2}));
+    
+    test0(S({1,2,3}), True,  S());
+    test0(S({1,2,3}), False, S({1,2,3}));
+}
+
+int main()
+{
+    test<std::forward_list<int>>();
+    test<std::forward_list<int, min_allocator<int>>> ();
+    test<std::forward_list<int, test_allocator<int>>> ();
+
+    test<std::forward_list<long>>();
+    test<std::forward_list<double>>();
+}
diff --git a/libcxx/test/std/containers/sequences/list/list.erasure/erase.pass.cpp b/libcxx/test/std/containers/sequences/list/list.erasure/erase.pass.cpp
new file mode 100644
index 00000000000..a9f65c0537e
--- /dev/null
+++ b/libcxx/test/std/containers/sequences/list/list.erasure/erase.pass.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <list>
+
+// template <class T, class Allocator, class U>
+//   void erase(list<T, Allocator>& c, const U& value);
+  
+
+#include <list>
+#include <optional>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class U>
+void
+test0(S s,  U val, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase(s, val)));
+    std::erase(s, val);
+    assert(s == expected);
+}
+
+template <class S>
+void test()
+{
+
+    test0(S(), 1, S());
+
+    test0(S({1}), 1, S());
+    test0(S({1}), 2, S({1}));
+
+    test0(S({1,2}), 1, S({2}));
+    test0(S({1,2}), 2, S({1}));
+    test0(S({1,2}), 3, S({1,2}));
+    test0(S({1,1}), 1, S());
+    test0(S({1,1}), 3, S({1,1}));
+
+    test0(S({1,2,3}), 1, S({2,3}));
+    test0(S({1,2,3}), 2, S({1,3}));
+    test0(S({1,2,3}), 3, S({1,2}));
+    test0(S({1,2,3}), 4, S({1,2,3}));
+
+    test0(S({1,1,1}), 1, S());
+    test0(S({1,1,1}), 2, S({1,1,1}));
+    test0(S({1,1,2}), 1, S({2}));
+    test0(S({1,1,2}), 2, S({1,1}));
+    test0(S({1,1,2}), 3, S({1,1,2}));
+    test0(S({1,2,2}), 1, S({2,2}));
+    test0(S({1,2,2}), 2, S({1}));
+    test0(S({1,2,2}), 3, S({1,2,2}));
+
+//  Test cross-type erasure
+    using opt = std::optional<typename S::value_type>;
+    test0(S({1,2,1}), opt(),  S({1,2,1}));
+    test0(S({1,2,1}), opt(1), S({2}));
+    test0(S({1,2,1}), opt(2), S({1,1}));
+    test0(S({1,2,1}), opt(3), S({1,2,1}));
+}
+
+int main()
+{
+    test<std::list<int>>();
+    test<std::list<int, min_allocator<int>>> ();
+    test<std::list<int, test_allocator<int>>> ();
+
+    test<std::list<long>>();
+    test<std::list<double>>();
+}
diff --git a/libcxx/test/std/containers/sequences/list/list.erasure/erase_if.pass.cpp b/libcxx/test/std/containers/sequences/list/list.erasure/erase_if.pass.cpp
new file mode 100644
index 00000000000..99b1c6530f9
--- /dev/null
+++ b/libcxx/test/std/containers/sequences/list/list.erasure/erase_if.pass.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <list>
+
+// template <class T, class Allocator, class Predicate>
+//   void erase_if(list<T, Allocator>& c, Predicate pred);  
+
+#include <list>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class Pred>
+void
+test0(S s, Pred p, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    assert(s == expected);
+}
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v == 1;};
+    auto is2 = [](auto v) { return v == 2;};
+    auto is3 = [](auto v) { return v == 3;};
+    auto is4 = [](auto v) { return v == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0(S(), is1, S());
+
+    test0(S({1}), is1, S());
+    test0(S({1}), is2, S({1}));
+
+    test0(S({1,2}), is1, S({2}));
+    test0(S({1,2}), is2, S({1}));
+    test0(S({1,2}), is3, S({1,2}));
+    test0(S({1,1}), is1, S());
+    test0(S({1,1}), is3, S({1,1}));
+
+    test0(S({1,2,3}), is1, S({2,3}));
+    test0(S({1,2,3}), is2, S({1,3}));
+    test0(S({1,2,3}), is3, S({1,2}));
+    test0(S({1,2,3}), is4, S({1,2,3}));
+
+    test0(S({1,1,1}), is1, S());
+    test0(S({1,1,1}), is2, S({1,1,1}));
+    test0(S({1,1,2}), is1, S({2}));
+    test0(S({1,1,2}), is2, S({1,1}));
+    test0(S({1,1,2}), is3, S({1,1,2}));
+    test0(S({1,2,2}), is1, S({2,2}));
+    test0(S({1,2,2}), is2, S({1}));
+    test0(S({1,2,2}), is3, S({1,2,2}));
+    
+    test0(S({1,2,3}), True,  S());
+    test0(S({1,2,3}), False, S({1,2,3}));
+}
+
+int main()
+{
+    test<std::list<int>>();
+    test<std::list<int, min_allocator<int>>> ();
+    test<std::list<int, test_allocator<int>>> ();
+
+    test<std::list<long>>();
+    test<std::list<double>>();
+}
diff --git a/libcxx/test/std/containers/sequences/vector/vector.erasure/erase.pass.cpp b/libcxx/test/std/containers/sequences/vector/vector.erasure/erase.pass.cpp
new file mode 100644
index 00000000000..e88252f1d92
--- /dev/null
+++ b/libcxx/test/std/containers/sequences/vector/vector.erasure/erase.pass.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <vector>
+
+// template <class T, class Allocator, class U>
+//   void erase(vector<T, Allocator>& c, const U& value);
+  
+
+#include <vector>
+#include <optional>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class U>
+void
+test0(S s,  U val, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase(s, val)));
+    std::erase(s, val);
+    assert(s == expected);
+}
+
+template <class S>
+void test()
+{
+
+    test0(S(), 1, S());
+
+    test0(S({1}), 1, S());
+    test0(S({1}), 2, S({1}));
+
+    test0(S({1,2}), 1, S({2}));
+    test0(S({1,2}), 2, S({1}));
+    test0(S({1,2}), 3, S({1,2}));
+    test0(S({1,1}), 1, S());
+    test0(S({1,1}), 3, S({1,1}));
+
+    test0(S({1,2,3}), 1, S({2,3}));
+    test0(S({1,2,3}), 2, S({1,3}));
+    test0(S({1,2,3}), 3, S({1,2}));
+    test0(S({1,2,3}), 4, S({1,2,3}));
+
+    test0(S({1,1,1}), 1, S());
+    test0(S({1,1,1}), 2, S({1,1,1}));
+    test0(S({1,1,2}), 1, S({2}));
+    test0(S({1,1,2}), 2, S({1,1}));
+    test0(S({1,1,2}), 3, S({1,1,2}));
+    test0(S({1,2,2}), 1, S({2,2}));
+    test0(S({1,2,2}), 2, S({1}));
+    test0(S({1,2,2}), 3, S({1,2,2}));
+
+//  Test cross-type erasure
+    using opt = std::optional<typename S::value_type>;
+    test0(S({1,2,1}), opt(),  S({1,2,1}));
+    test0(S({1,2,1}), opt(1), S({2}));
+    test0(S({1,2,1}), opt(2), S({1,1}));
+    test0(S({1,2,1}), opt(3), S({1,2,1}));
+}
+
+int main()
+{
+    test<std::vector<int>>();
+    test<std::vector<int, min_allocator<int>>> ();
+    test<std::vector<int, test_allocator<int>>> ();
+
+    test<std::vector<long>>();
+    test<std::vector<double>>();
+}
diff --git a/libcxx/test/std/containers/sequences/vector/vector.erasure/erase_if.pass.cpp b/libcxx/test/std/containers/sequences/vector/vector.erasure/erase_if.pass.cpp
new file mode 100644
index 00000000000..8025a34071f
--- /dev/null
+++ b/libcxx/test/std/containers/sequences/vector/vector.erasure/erase_if.pass.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <vector>
+
+// template <class T, class Allocator, class Predicate>
+//   void erase_if(vector<T, Allocator>& c, Predicate pred);  
+
+#include <vector>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class Pred>
+void
+test0(S s, Pred p, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    assert(s == expected);
+}
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v == 1;};
+    auto is2 = [](auto v) { return v == 2;};
+    auto is3 = [](auto v) { return v == 3;};
+    auto is4 = [](auto v) { return v == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0(S(), is1, S());
+
+    test0(S({1}), is1, S());
+    test0(S({1}), is2, S({1}));
+
+    test0(S({1,2}), is1, S({2}));
+    test0(S({1,2}), is2, S({1}));
+    test0(S({1,2}), is3, S({1,2}));
+    test0(S({1,1}), is1, S());
+    test0(S({1,1}), is3, S({1,1}));
+
+    test0(S({1,2,3}), is1, S({2,3}));
+    test0(S({1,2,3}), is2, S({1,3}));
+    test0(S({1,2,3}), is3, S({1,2}));
+    test0(S({1,2,3}), is4, S({1,2,3}));
+
+    test0(S({1,1,1}), is1, S());
+    test0(S({1,1,1}), is2, S({1,1,1}));
+    test0(S({1,1,2}), is1, S({2}));
+    test0(S({1,1,2}), is2, S({1,1}));
+    test0(S({1,1,2}), is3, S({1,1,2}));
+    test0(S({1,2,2}), is1, S({2,2}));
+    test0(S({1,2,2}), is2, S({1}));
+    test0(S({1,2,2}), is3, S({1,2,2}));
+    
+    test0(S({1,2,3}), True,  S());
+    test0(S({1,2,3}), False, S({1,2,3}));
+}
+
+int main()
+{
+    test<std::vector<int>>();
+    test<std::vector<int, min_allocator<int>>> ();
+    test<std::vector<int, test_allocator<int>>> ();
+
+    test<std::vector<long>>();
+    test<std::vector<double>>();
+}
diff --git a/libcxx/test/std/containers/unord/unord.map/erase_if.pass.cpp b/libcxx/test/std/containers/unord/unord.map/erase_if.pass.cpp
new file mode 100644
index 00000000000..f6a580c2160
--- /dev/null
+++ b/libcxx/test/std/containers/unord/unord.map/erase_if.pass.cpp
@@ -0,0 +1,80 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <unordered_map>
+
+// template <class Key, class T, class Hash, class Pred, class Allocator, class Predicate>
+//   void erase_if(unordered_map<Key, T, Hash, Pred, Allocator>& c, Predicate pred);
+
+#include <unordered_map>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+using Init = std::initializer_list<int>;
+template <typename M>
+M make (Init vals)
+{
+    M ret;
+    for (int v : vals)
+        ret[v] = v + 10;
+    return ret;
+}
+
+template <typename M, typename Pred>
+void
+test0(Init vals, Pred p, Init expected)
+{
+    M s = make<M> (vals);
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    M e = make<M>(expected);
+    assert((std::is_permutation(s.begin(), s.end(), e.begin(), e.end())));
+}
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v.first == 1;};
+    auto is2 = [](auto v) { return v.first == 2;};
+    auto is3 = [](auto v) { return v.first == 3;};
+    auto is4 = [](auto v) { return v.first == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0<S>({}, is1, {});
+
+    test0<S>({1}, is1, {});
+    test0<S>({1}, is2, {1});
+
+    test0<S>({1,2}, is1, {2});
+    test0<S>({1,2}, is2, {1});
+    test0<S>({1,2}, is3, {1,2});
+
+    test0<S>({1,2,3}, is1, {2,3});
+    test0<S>({1,2,3}, is2, {1,3});
+    test0<S>({1,2,3}, is3, {1,2});
+    test0<S>({1,2,3}, is4, {1,2,3});
+
+    test0<S>({1,2,3}, True,  {});
+    test0<S>({1,2,3}, False, {1,2,3});
+}
+
+int main()
+{
+    test<std::unordered_map<int, int>>();
+    test<std::unordered_map<int, int, std::hash<int>, std::equal_to<int>, min_allocator<std::pair<const int, int>>>> ();
+    test<std::unordered_map<int, int, std::hash<int>, std::equal_to<int>, test_allocator<std::pair<const int, int>>>> ();
+
+    test<std::unordered_map<long, short>>();
+    test<std::unordered_map<short, double>>();
+}
+
diff --git a/libcxx/test/std/containers/unord/unord.multimap/erase_if.pass.cpp b/libcxx/test/std/containers/unord/unord.multimap/erase_if.pass.cpp
new file mode 100644
index 00000000000..dc613269a35
--- /dev/null
+++ b/libcxx/test/std/containers/unord/unord.multimap/erase_if.pass.cpp
@@ -0,0 +1,90 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <unordered_map>
+
+// template <class Key, class T, class Hash, class Pred, class Allocator, class Predicate>
+//   void erase_if(unordered_multimap<Key, T, Hash, Pred, Allocator>& c, Predicate pred);
+
+#include <unordered_map>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+using Init = std::initializer_list<int>;
+template <typename M>
+M make (Init vals)
+{
+    M ret;
+    for (int v : vals)
+        ret.insert(typename M::value_type(v, v + 10));
+    return ret;
+}
+
+template <typename M, typename Pred>
+void
+test0(Init vals, Pred p, Init expected)
+{
+    M s = make<M> (vals);
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    M e = make<M>(expected);
+    assert((std::is_permutation(s.begin(), s.end(), e.begin(), e.end())));
+}
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v.first == 1;};
+    auto is2 = [](auto v) { return v.first == 2;};
+    auto is3 = [](auto v) { return v.first == 3;};
+    auto is4 = [](auto v) { return v.first == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0<S>({}, is1, {});
+
+    test0<S>({1}, is1, {});
+    test0<S>({1}, is2, {1});
+
+    test0<S>({1,2}, is1, {2});
+    test0<S>({1,2}, is2, {1});
+    test0<S>({1,2}, is3, {1,2});
+    test0<S>({1,1}, is1, {});
+    test0<S>({1,1}, is3, {1,1});
+
+    test0<S>({1,2,3}, is1, {2,3});
+    test0<S>({1,2,3}, is2, {1,3});
+    test0<S>({1,2,3}, is3, {1,2});
+    test0<S>({1,2,3}, is4, {1,2,3});
+
+    test0<S>({1,1,1}, is1, {});
+    test0<S>({1,1,1}, is2, {1,1,1});
+    test0<S>({1,1,2}, is1, {2});
+    test0<S>({1,1,2}, is2, {1,1});
+    test0<S>({1,1,2}, is3, {1,1,2});
+    test0<S>({1,2,2}, is1, {2,2});
+    test0<S>({1,2,2}, is2, {1});
+    test0<S>({1,2,2}, is3, {1,2,2});
+    
+    test0<S>({1,2,3}, True,  {});
+    test0<S>({1,2,3}, False, {1,2,3});
+}
+
+int main()
+{
+    test<std::unordered_multimap<int, int>>();
+    test<std::unordered_multimap<int, int, std::hash<int>, std::equal_to<int>, min_allocator<std::pair<const int, int>>>> ();
+    test<std::unordered_multimap<int, int, std::hash<int>, std::equal_to<int>, test_allocator<std::pair<const int, int>>>> ();
+
+    test<std::unordered_multimap<long, short>>();
+    test<std::unordered_multimap<short, double>>();
+}
diff --git a/libcxx/test/std/containers/unord/unord.multiset/erase_if.pass.cpp b/libcxx/test/std/containers/unord/unord.multiset/erase_if.pass.cpp
new file mode 100644
index 00000000000..7a9d93d432f
--- /dev/null
+++ b/libcxx/test/std/containers/unord/unord.multiset/erase_if.pass.cpp
@@ -0,0 +1,91 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <set>
+
+// template <class T, class Hash, class Compare, class Allocator, class Predicate>
+//   void erase_if(unordered_multiset<T, Hash, Compare, Allocator>& c, Predicate pred);
+
+#include <unordered_set>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+using Init = std::initializer_list<int>;
+
+template <typename M>
+M make (Init vals)
+{
+    M ret;
+    for (int v : vals)
+        ret.insert(v);
+    return ret;
+}
+
+template <typename M, typename Pred>
+void
+test0(Init vals, Pred p, Init expected)
+{
+    M s = make<M> (vals);
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    M e = make<M>(expected);
+    assert((std::is_permutation(s.begin(), s.end(), e.begin(), e.end())));
+}
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v == 1;};
+    auto is2 = [](auto v) { return v == 2;};
+    auto is3 = [](auto v) { return v == 3;};
+    auto is4 = [](auto v) { return v == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0<S>({}, is1, {});
+
+    test0<S>({1}, is1, {});
+    test0<S>({1}, is2, {1});
+
+    test0<S>({1,2}, is1, {2});
+    test0<S>({1,2}, is2, {1});
+    test0<S>({1,2}, is3, {1,2});
+    test0<S>({1,1}, is1, {});
+    test0<S>({1,1}, is3, {1,1});
+
+    test0<S>({1,2,3}, is1, {2,3});
+    test0<S>({1,2,3}, is2, {1,3});
+    test0<S>({1,2,3}, is3, {1,2});
+    test0<S>({1,2,3}, is4, {1,2,3});
+
+    test0<S>({1,1,1}, is1, {});
+    test0<S>({1,1,1}, is2, {1,1,1});
+    test0<S>({1,1,2}, is1, {2});
+    test0<S>({1,1,2}, is2, {1,1});
+    test0<S>({1,1,2}, is3, {1,1,2});
+    test0<S>({1,2,2}, is1, {2,2});
+    test0<S>({1,2,2}, is2, {1});
+    test0<S>({1,2,2}, is3, {1,2,2});
+    
+    test0<S>({1,2,3}, True,  {});
+    test0<S>({1,2,3}, False, {1,2,3});
+}
+
+int main()
+{
+    test<std::unordered_multiset<int>>();
+    test<std::unordered_multiset<int, std::hash<int>, std::equal_to<int>, min_allocator<int>>> ();
+    test<std::unordered_multiset<int, std::hash<int>, std::equal_to<int>, test_allocator<int>>> ();
+
+    test<std::unordered_multiset<long>>();
+    test<std::unordered_multiset<double>>();
+}
diff --git a/libcxx/test/std/containers/unord/unord.set/erase_if.pass.cpp b/libcxx/test/std/containers/unord/unord.set/erase_if.pass.cpp
new file mode 100644
index 00000000000..e060fda1fe8
--- /dev/null
+++ b/libcxx/test/std/containers/unord/unord.set/erase_if.pass.cpp
@@ -0,0 +1,81 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <unordered_set>
+
+// template <class T, class Hash, class Compare, class Allocator, class Predicate>
+//   void erase_if(unorderd_set<T, Hash, Compare, Allocator>& c, Predicate pred);
+
+#include <unordered_set>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+using Init = std::initializer_list<int>;
+
+template <typename M>
+M make (Init vals)
+{
+    M ret;
+    for (int v : vals)
+        ret.insert(v);
+    return ret;
+}
+
+template <typename M, typename Pred>
+void
+test0(Init vals, Pred p, Init expected)
+{
+    M s = make<M> (vals);
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    M e = make<M>(expected);
+    assert((std::is_permutation(s.begin(), s.end(), e.begin(), e.end())));
+}
+
+
+template <typename S>
+void test()
+{
+    auto is1 = [](auto v) { return v == 1;};
+    auto is2 = [](auto v) { return v == 2;};
+    auto is3 = [](auto v) { return v == 3;};
+    auto is4 = [](auto v) { return v == 4;};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0<S>({}, is1, {});
+
+    test0<S>({1}, is1, {});
+    test0<S>({1}, is2, {1});
+
+    test0<S>({1,2}, is1, {2});
+    test0<S>({1,2}, is2, {1});
+    test0<S>({1,2}, is3, {1,2});
+
+    test0<S>({1,2,3}, is1, {2,3});
+    test0<S>({1,2,3}, is2, {1,3});
+    test0<S>({1,2,3}, is3, {1,2});
+    test0<S>({1,2,3}, is4, {1,2,3});
+
+    test0<S>({1,2,3}, True,  {});
+    test0<S>({1,2,3}, False, {1,2,3});
+}
+
+int main()
+{
+    test<std::unordered_set<int>>();
+    test<std::unordered_set<int, std::hash<int>, std::equal_to<int>, min_allocator<int>>> ();
+    test<std::unordered_set<int, std::hash<int>, std::equal_to<int>, test_allocator<int>>> ();
+
+    test<std::unordered_set<long>>();
+    test<std::unordered_set<double>>();
+}
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/deque.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/deque.version.pass.cpp
index d3ca7d9b02c..188d2f3c0ac 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/deque.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/deque.version.pass.cpp
@@ -12,6 +12,7 @@
 
 /*  Constant                                    Value
     __cpp_lib_allocator_traits_is_always_equal  201411L
+    __cpp_lib_erase_if                          201811L
     __cpp_lib_nonmember_container_access        201411L
 
 */
@@ -24,6 +25,16 @@ int main()
 {
 //  ensure that the macros that are supposed to be defined in <deque> are defined.
 
+#if TEST_STD_VER > 17
+# if !defined(__cpp_lib_erase_if)  
+  LIBCPP_STATIC_ASSERT(false, "__cpp_lib_erase_if is not defined");
+# else
+#  if __cpp_lib_erase_if < 201811L
+#   error "__cpp_lib_erase_if has an invalid value"
+#  endif
+# endif
+#endif
+
 /*
 #if !defined(__cpp_lib_fooby)
 # error "__cpp_lib_fooby is not defined"
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/forward_list.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/forward_list.version.pass.cpp
index 73c8462ca3f..9b44f6e2c46 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/forward_list.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/forward_list.version.pass.cpp
@@ -12,6 +12,7 @@
 
 /*  Constant                                    Value
     __cpp_lib_allocator_traits_is_always_equal  201411L
+    __cpp_lib_erase_if                          201811L
     __cpp_lib_incomplete_container_elements     201505L
     __cpp_lib_list_remove_return_type           201806L
     __cpp_lib_nonmember_container_access        201411L
@@ -26,6 +27,16 @@ int main()
 {
 //  ensure that the macros that are supposed to be defined in <forward_list> are defined.
 
+#if TEST_STD_VER > 17
+# if !defined(__cpp_lib_erase_if)  
+  LIBCPP_STATIC_ASSERT(false, "__cpp_lib_erase_if is not defined");
+# else
+#  if __cpp_lib_erase_if < 201811L
+#   error "__cpp_lib_erase_if has an invalid value"
+#  endif
+# endif
+#endif
+
 /*
 #if !defined(__cpp_lib_fooby)
 # error "__cpp_lib_fooby is not defined"
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/list.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/list.version.pass.cpp
index 3db7995633f..e6e65655b92 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/list.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/list.version.pass.cpp
@@ -12,6 +12,7 @@
 
 /*  Constant                                    Value
     __cpp_lib_allocator_traits_is_always_equal  201411L
+    __cpp_lib_erase_if                          201811L
     __cpp_lib_incomplete_container_elements     201505L
     __cpp_lib_list_remove_return_type           201806L
     __cpp_lib_nonmember_container_access        201411L
@@ -26,6 +27,16 @@ int main()
 {
 //  ensure that the macros that are supposed to be defined in <list> are defined.
 
+#if TEST_STD_VER > 17
+# if !defined(__cpp_lib_erase_if)  
+  LIBCPP_STATIC_ASSERT(false, "__cpp_lib_erase_if is not defined");
+# else
+#  if __cpp_lib_erase_if < 201811L
+#   error "__cpp_lib_erase_if has an invalid value"
+#  endif
+# endif
+#endif
+
 /*
 #if !defined(__cpp_lib_fooby)
 # error "__cpp_lib_fooby is not defined"
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/map.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/map.version.pass.cpp
index ffcc003e3a0..e7dbf7d20f0 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/map.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/map.version.pass.cpp
@@ -12,6 +12,7 @@
 
 /*  Constant                                    Value
     __cpp_lib_allocator_traits_is_always_equal  201411L
+    __cpp_lib_erase_if                          201811L
     __cpp_lib_generic_associative_lookup        201304L
     __cpp_lib_map_try_emplace                   201411L
     __cpp_lib_node_extract                      201606L
@@ -27,6 +28,16 @@ int main()
 {
 //  ensure that the macros that are supposed to be defined in <map> are defined.
 
+#if TEST_STD_VER > 17
+# if !defined(__cpp_lib_erase_if)  
+  LIBCPP_STATIC_ASSERT(false, "__cpp_lib_erase_if is not defined");
+# else
+#  if __cpp_lib_erase_if < 201811L
+#   error "__cpp_lib_erase_if has an invalid value"
+#  endif
+# endif
+#endif
+
 /*
 #if !defined(__cpp_lib_fooby)
 # error "__cpp_lib_fooby is not defined"
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/set.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/set.version.pass.cpp
index 96918031d37..716eae6d9f0 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/set.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/set.version.pass.cpp
@@ -12,6 +12,7 @@
 
 /*  Constant                                    Value
     __cpp_lib_allocator_traits_is_always_equal  201411L
+    __cpp_lib_erase_if                          201811L
     __cpp_lib_generic_associative_lookup        201304L
     __cpp_lib_node_extract                      201606L
     __cpp_lib_nonmember_container_access        201411L
@@ -26,6 +27,16 @@ int main()
 {
 //  ensure that the macros that are supposed to be defined in <set> are defined.
 
+#if TEST_STD_VER > 17
+# if !defined(__cpp_lib_erase_if)  
+  LIBCPP_STATIC_ASSERT(false, "__cpp_lib_erase_if is not defined");
+# else
+#  if __cpp_lib_erase_if < 201811L
+#   error "__cpp_lib_erase_if has an invalid value"
+#  endif
+# endif
+#endif
+
 /*
 #if !defined(__cpp_lib_fooby)
 # error "__cpp_lib_fooby is not defined"
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/string.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/string.version.pass.cpp
index 2f408b9886e..87e8c8f96c3 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/string.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/string.version.pass.cpp
@@ -12,6 +12,7 @@
 
 /*  Constant                                    Value
     __cpp_lib_allocator_traits_is_always_equal  201411L
+    __cpp_lib_erase_if                          201811L
     __cpp_lib_char8_t                           201811L
     __cpp_lib_nonmember_container_access        201411L
     __cpp_lib_string_udls                       201304L
@@ -27,6 +28,16 @@ int main()
 {
 //  ensure that the macros that are supposed to be defined in <string> are defined.
 
+#if TEST_STD_VER > 17
+# if !defined(__cpp_lib_erase_if)  
+  LIBCPP_STATIC_ASSERT(false, "__cpp_lib_erase_if is not defined");
+# else
+#  if __cpp_lib_erase_if < 201811L
+#   error "__cpp_lib_erase_if has an invalid value"
+#  endif
+# endif
+#endif
+
 #if TEST_STD_VER > 17 && defined(__cpp_char8_t)
 # if !defined(__cpp_lib_char8_t)  
   LIBCPP_STATIC_ASSERT(false, "__cpp_lib_char8_t is not defined");
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/unordered_map.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/unordered_map.version.pass.cpp
index 38e01171731..d23a91a3091 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/unordered_map.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/unordered_map.version.pass.cpp
@@ -12,6 +12,7 @@
 
 /*  Constant                                    Value
     __cpp_lib_allocator_traits_is_always_equal  201411L
+    __cpp_lib_erase_if                          201811L
     __cpp_lib_node_extract                      201606L
     __cpp_lib_nonmember_container_access        201411L
     __cpp_lib_unordered_map_try_emplace         201411L
@@ -26,6 +27,17 @@ int main()
 {
 //  ensure that the macros that are supposed to be defined in <unordered_map> are defined.
 
+#if TEST_STD_VER > 17
+# if !defined(__cpp_lib_erase_if)  
+  LIBCPP_STATIC_ASSERT(false, "__cpp_lib_erase_if is not defined");
+# else
+#  if __cpp_lib_erase_if < 201811L
+#   error "__cpp_lib_erase_if has an invalid value"
+#  endif
+# endif
+#endif
+
+
 /*
 #if !defined(__cpp_lib_fooby)
 # error "__cpp_lib_fooby is not defined"
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/unordered_set.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/unordered_set.version.pass.cpp
index 762a07c372a..c4dbed14b9c 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/unordered_set.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/unordered_set.version.pass.cpp
@@ -12,6 +12,7 @@
 
 /*  Constant                                    Value
     __cpp_lib_allocator_traits_is_always_equal  201411L
+    __cpp_lib_erase_if                          201811L
     __cpp_lib_node_extract                      201606L
     __cpp_lib_nonmember_container_access        201411L
 
@@ -25,6 +26,16 @@ int main()
 {
 //  ensure that the macros that are supposed to be defined in <unordered_set> are defined.
 
+#if TEST_STD_VER > 17
+# if !defined(__cpp_lib_erase_if)  
+  LIBCPP_STATIC_ASSERT(false, "__cpp_lib_erase_if is not defined");
+# else
+#  if __cpp_lib_erase_if < 201811L
+#   error "__cpp_lib_erase_if has an invalid value"
+#  endif
+# endif
+#endif
+
 /*
 #if !defined(__cpp_lib_fooby)
 # error "__cpp_lib_fooby is not defined"
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/vector.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/vector.version.pass.cpp
index 9932a61c56d..e7cb1942c0b 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/vector.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/vector.version.pass.cpp
@@ -12,6 +12,7 @@
 
 /*  Constant                                    Value
     __cpp_lib_allocator_traits_is_always_equal  201411L
+    __cpp_lib_erase_if                          201811L
     __cpp_lib_incomplete_container_elements     201505L
     __cpp_lib_nonmember_container_access        201411L
 
@@ -25,6 +26,16 @@ int main()
 {
 //  ensure that the macros that are supposed to be defined in <vector> are defined.
 
+#if TEST_STD_VER > 17
+# if !defined(__cpp_lib_erase_if)  
+  LIBCPP_STATIC_ASSERT(false, "__cpp_lib_erase_if is not defined");
+# else
+#  if __cpp_lib_erase_if < 201811L
+#   error "__cpp_lib_erase_if has an invalid value"
+#  endif
+# endif
+#endif
+
 /*
 #if !defined(__cpp_lib_fooby)
 # error "__cpp_lib_fooby is not defined"
diff --git a/libcxx/test/std/strings/strings.erasure/erase.pass.cpp b/libcxx/test/std/strings/strings.erasure/erase.pass.cpp
new file mode 100644
index 00000000000..657a56c7315
--- /dev/null
+++ b/libcxx/test/std/strings/strings.erasure/erase.pass.cpp
@@ -0,0 +1,76 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <string>
+
+// template <class charT, class traits, class Allocator, class U>
+//   void erase(basic_string<charT, traits, Allocator>& c, const U& value);
+  
+
+#include <string>
+#include <optional>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class U>
+void
+test0(S s,  U val, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase(s, val)));
+    std::erase(s, val);
+    LIBCPP_ASSERT(s.__invariants());
+    assert(s == expected);
+}
+
+template <class S>
+void test()
+{
+
+    test0(S(""), 'a', S(""));
+
+    test0(S("a"), 'a', S(""));
+    test0(S("a"), 'b', S("a"));
+
+    test0(S("ab"), 'a', S("b"));
+    test0(S("ab"), 'b', S("a"));
+    test0(S("ab"), 'c', S("ab"));
+    test0(S("aa"), 'a', S(""));
+    test0(S("aa"), 'c', S("aa"));
+
+    test0(S("abc"), 'a', S("bc"));
+    test0(S("abc"), 'b', S("ac"));
+    test0(S("abc"), 'c', S("ab"));
+    test0(S("abc"), 'd', S("abc"));
+
+    test0(S("aab"), 'a', S("b"));
+    test0(S("aab"), 'b', S("aa"));
+    test0(S("aab"), 'c', S("aab"));
+    test0(S("abb"), 'a', S("bb"));
+    test0(S("abb"), 'b', S("a"));
+    test0(S("abb"), 'c', S("abb"));
+    test0(S("aaa"), 'a', S(""));
+    test0(S("aaa"), 'b', S("aaa"));
+
+//  Test cross-type erasure
+    using opt = std::optional<typename S::value_type>;
+    test0(S("aba"), opt(),    S("aba"));
+    test0(S("aba"), opt('a'), S("b"));
+    test0(S("aba"), opt('b'), S("aa"));
+    test0(S("aba"), opt('c'), S("aba"));
+}
+
+int main()
+{
+    test<std::string>();
+    test<std::basic_string<char, std::char_traits<char>, min_allocator<char>>> ();
+    test<std::basic_string<char, std::char_traits<char>, test_allocator<char>>> ();
+}
diff --git a/libcxx/test/std/strings/strings.erasure/erase_if.pass.cpp b/libcxx/test/std/strings/strings.erasure/erase_if.pass.cpp
new file mode 100644
index 00000000000..d7014868fd3
--- /dev/null
+++ b/libcxx/test/std/strings/strings.erasure/erase_if.pass.cpp
@@ -0,0 +1,76 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <string>
+
+// template <class charT, class traits, class Allocator, class Predicate>
+//   void erase_if(basic_string<charT, traits, Allocator>& c, Predicate pred);  
+
+#include <string>
+
+#include "test_macros.h"
+#include "test_allocator.h"
+#include "min_allocator.h"
+
+template <class S, class Pred>
+void
+test0(S s, Pred p, S expected)
+{
+    ASSERT_SAME_TYPE(void, decltype(std::erase_if(s, p)));
+    std::erase_if(s, p);
+    LIBCPP_ASSERT(s.__invariants());
+    assert(s == expected);
+}
+
+template <typename S>
+void test()
+{
+    auto isA = [](auto ch) { return ch == 'a';};
+    auto isB = [](auto ch) { return ch == 'b';};
+    auto isC = [](auto ch) { return ch == 'c';};
+    auto isD = [](auto ch) { return ch == 'd';};
+    auto True  = [](auto) { return true; };
+    auto False = [](auto) { return false; };
+    
+    test0(S(""), isA, S(""));
+
+    test0(S("a"), isA, S(""));
+    test0(S("a"), isB, S("a"));
+
+    test0(S("ab"), isA, S("b"));
+    test0(S("ab"), isB, S("a"));
+    test0(S("ab"), isC, S("ab"));
+    test0(S("aa"), isA, S(""));
+    test0(S("aa"), isC, S("aa"));
+
+    test0(S("abc"), isA, S("bc"));
+    test0(S("abc"), isB, S("ac"));
+    test0(S("abc"), isC, S("ab"));
+    test0(S("abc"), isD, S("abc"));
+
+    test0(S("aab"), isA, S("b"));
+    test0(S("aab"), isB, S("aa"));
+    test0(S("aab"), isC, S("aab"));
+    test0(S("abb"), isA, S("bb"));
+    test0(S("abb"), isB, S("a"));
+    test0(S("abb"), isC, S("abb"));
+    test0(S("aaa"), isA, S(""));
+    test0(S("aaa"), isB, S("aaa"));
+
+    test0(S("aba"), False,  S("aba"));
+    test0(S("aba"), True,   S(""));
+}
+
+int main()
+{
+    test<std::string>();
+    test<std::basic_string<char, std::char_traits<char>, min_allocator<char>>> ();
+    test<std::basic_string<char, std::char_traits<char>, test_allocator<char>>> ();
+}