util: New macro CONST_CAST.

Casts are sometimes necessary.  One common reason that they are necessary
is for discarding a "const" qualifier.  However, this can impede
maintenance: if the type of the expression being cast changes, then the
presence of the cast can hide a necessary change in the code that does the
cast.  Using CONST_CAST, instead of a bare cast, makes these changes
visible.

Inspired by my own work elsewhere:
http://git.savannah.gnu.org/cgit/pspp.git/tree/src/libpspp/cast.h#n80

Signed-off-by: Ben Pfaff <blp@nicira.com>

3 files changed, 13 insertions, 13 deletions

diff --git a/ovsdb/ovsdb-server.c b/ovsdb/ovsdb-server.c
index 6c68e506..1bf10d9b 100644
--- a/ovsdb/ovsdb-server.c
+++ b/ovsdb/ovsdb-server.c
@@ -350,8 +350,8 @@ read_map_string_column(const struct ovsdb_row *row, const char *column_name,
     union ovsdb_atom *atom_key = NULL, *atom_value = NULL;
     size_t i;
 
-    datum = get_datum((struct ovsdb_row *) row, column_name, OVSDB_TYPE_STRING,
-                      OVSDB_TYPE_STRING, UINT_MAX);
+    datum = get_datum(CONST_CAST(struct ovsdb_row *, row), column_name,
+                      OVSDB_TYPE_STRING, OVSDB_TYPE_STRING, UINT_MAX);
 
     if (!datum) {
         return NULL;
@@ -374,8 +374,8 @@ read_column(const struct ovsdb_row *row, const char *column_name,
 {
     const struct ovsdb_datum *datum;
 
-    datum = get_datum((struct ovsdb_row *) row, column_name, type, OVSDB_TYPE_VOID,
-                      1);
+    datum = get_datum(CONST_CAST(struct ovsdb_row *, row), column_name, type,
+                      OVSDB_TYPE_VOID, 1);
     return datum && datum->n ? datum->keys : NULL;
 }
 
diff --git a/ovsdb/row.c b/ovsdb/row.c
index 457869b3..450c3274 100644
--- a/ovsdb/row.c
+++ b/ovsdb/row.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2009, 2010, 2011 Nicira, Inc.
+/* Copyright (c) 2009, 2010, 2011, 2012 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -36,7 +36,7 @@ allocate_row(const struct ovsdb_table *table)
                        + sizeof(struct ovsdb_datum) * n_fields
                        + sizeof(struct hmap_node) * n_indexes);
     struct ovsdb_row *row = xmalloc(row_size);
-    row->table = (struct ovsdb_table *) table;
+    row->table = CONST_CAST(struct ovsdb_table *, table);
     row->txn_row = NULL;
     list_init(&row->src_refs);
     list_init(&row->dst_refs);
@@ -347,7 +347,7 @@ ovsdb_row_hash_destroy(struct ovsdb_row_hash *rh, bool destroy_rows)
     HMAP_FOR_EACH_SAFE (node, next, hmap_node, &rh->rows) {
         hmap_remove(&rh->rows, &node->hmap_node);
         if (destroy_rows) {
-            ovsdb_row_destroy((struct ovsdb_row *) node->row);
+            ovsdb_row_destroy(CONST_CAST(struct ovsdb_row *, node->row));
         }
         free(node);
     }
diff --git a/ovsdb/transaction.c b/ovsdb/transaction.c
index e785e216..cc890ad8 100644
--- a/ovsdb/transaction.c
+++ b/ovsdb/transaction.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2009, 2010, 2011 Nicira, Inc.
+/* Copyright (c) 2009, 2010, 2011, 2012 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -439,8 +439,8 @@ static void
 add_weak_ref(struct ovsdb_txn *txn,
              const struct ovsdb_row *src_, const struct ovsdb_row *dst_)
 {
-    struct ovsdb_row *src = (struct ovsdb_row *) src_;
-    struct ovsdb_row *dst = (struct ovsdb_row *) dst_;
+    struct ovsdb_row *src = CONST_CAST(struct ovsdb_row *, src_);
+    struct ovsdb_row *dst = CONST_CAST(struct ovsdb_row *, dst_);
     struct ovsdb_weak_ref *weak;
 
     if (src == dst) {
@@ -864,7 +864,7 @@ ovsdb_txn_row_create(struct ovsdb_txn *txn, struct ovsdb_table *table,
                      const struct ovsdb_row *old_, struct ovsdb_row *new)
 {
     const struct ovsdb_row *row = old_ ? old_ : new;
-    struct ovsdb_row *old = (struct ovsdb_row *) old_;
+    struct ovsdb_row *old = CONST_CAST(struct ovsdb_row *, old_);
     size_t n_columns = shash_count(&table->schema->columns);
     struct ovsdb_txn_table *txn_table;
     struct ovsdb_txn_row *txn_row;
@@ -895,7 +895,7 @@ ovsdb_txn_row_create(struct ovsdb_txn *txn, struct ovsdb_table *table,
 struct ovsdb_row *
 ovsdb_txn_row_modify(struct ovsdb_txn *txn, const struct ovsdb_row *ro_row_)
 {
-    struct ovsdb_row *ro_row = (struct ovsdb_row *) ro_row_;
+    struct ovsdb_row *ro_row = CONST_CAST(struct ovsdb_row *, ro_row_);
 
     if (ro_row->txn_row) {
         assert(ro_row == ro_row->txn_row->new);
@@ -931,7 +931,7 @@ ovsdb_txn_row_insert(struct ovsdb_txn *txn, struct ovsdb_row *row)
 void
 ovsdb_txn_row_delete(struct ovsdb_txn *txn, const struct ovsdb_row *row_)
 {
-    struct ovsdb_row *row = (struct ovsdb_row *) row_;
+    struct ovsdb_row *row = CONST_CAST(struct ovsdb_row *, row_);
     struct ovsdb_table *table = row->table;
     struct ovsdb_txn_row *txn_row = row->txn_row;