[[types]] === Data Types Painless supports both dynamic and static types. Static types are split into _primitive types_ and _reference types_. [[dynamic-types]] ==== Dynamic Types Painless supports one dynamic type: `def`. The `def` type can represent any primitive or reference type. When you use the `def` type, it mimics the exact behavior of whatever type it represents at runtime. The default value for the def type is `null.` Internally, if the `def` type represents a primitive type, it is converted to the corresponding reference type. It still behaves like the primitive type, however, including within the casting model. The `def` type can be assigned to different types during the course of script execution. IMPORTANT: Because a `def` type variable can be assigned to different types during execution, type conversion errors that occur when using the `def` type happen at runtime. Using the `def` type can have a slight impact on performance. If performance is critical, it's better to declare static types. *Examples:* [source,Java] ---- def x = 1; // Declare def variable x and set it to the // literal int 1 def l = new ArrayList(); // Declare def variable l and set it a newly // allocated ArrayList ---- [[primitive-types]] ==== Primitive Types Primitive types are allocated directly onto the stack according to the standard Java memory model. Primitive types can behave as their corresponding (<>) reference type. This means any piece of a reference type can be accessed or called through the primitive type. Operations performed in this manner convert the primitive type to its corresponding reference type at runtime and perform the field access or method call without needing to perform any other operations. Painless supports the following primitive types. byte:: An 8-bit, signed, two's complement integer. Range: [-128, 127]. Default value: 0. Reference type: Byte. short:: A 16-bit, signed, two's complement integer. Range: [-32768, 32767]. Default value: 0. Reference type: Short. char:: A 16-bit Unicode character. Range: [0, 65535]. Default value: 0 or `\u0000`. Reference type: Character. int:: A 32-bit, signed, two's complement integer. Range: [-2^32, 2^32-1]. Default value: 0. Reference type: Integer. long:: A 64-bit, signed, two's complement integer. Range: [-2^64, 2^64-1]. Default value: 0. Reference type: Long. float:: A 32-bit, single-precision, IEEE 754 floating point number. Range: Depends on multiple factors. Default value: 0.0. Reference type: Float. double:: A 64-bit, double-precision, IEEE 754 floating point number. Range: Depends on multiple factors. Default value: 0.0. Reference type: Double. boolean:: A logical quanity with two possible values: true and false. Range: true/false. Default value: false. Reference type: Boolean. *Examples:* [source,Java] ---- int i = 1; // Declare variable i as an int and set it to the // literal 1 double d; // Declare variable d as a double and set it to the // default value of 0.0 boolean b = true; // Declare variable b as a boolean and set it to true ---- Using methods from the corresponding reference type on a primitive type. [source,Java] ---- int i = 1; // Declare variable i as an int and set it to the // literal 1 i.toString(); // Invokes the Integer method toString on variable i ---- [[reference-types]] ==== Reference Types Reference types are similar to Java classes and can contain multiple pieces known as _members_. However, reference types do not support access modifiers. You allocate reference type instances on the heap using the `new` operator. Reference types can have both static and non-static members: * Static members are shared by all instances of the same reference type and can be accessed without allocating an instance of the reference type. For example `Integer.MAX_VALUE`. * Non-static members are specific to an instance of the reference type and can only be accessed through the allocated instance. The default value for a reference type is `null`, indicating that no memory has been allocated for it. When you assign `null` to a reference type, its previous value is discarded and garbage collected in accordance with the Java memory model as long as there are no other references to that value. A reference type can contain: * Zero to many primitive types. Primitive type members can be static or non-static and read-only or read-write. * Zero to many reference types. Reference type members can be static or non-static and read-only or read-write. * Methods that call an internal function to return a value and/or manipulate the primitive or reference type members. Method members can be static or non-static. * Constructors that call an internal function to return a newly-allocated reference type instance. Constructors are non-static methods that can optionally manipulate the primitive and reference type members. Reference types support a Java-style inheritance model. Consider types A and B. Type A is considered to be a parent of B, and B a child of A, if B inherits (is able to access as its own) all of A's fields and methods. Type B is considered a descendant of A if there exists a recursive parent-child relationship from B to A with none to many types in between. In this case, B inherits all of A's fields and methods along with all of the fields and methods of the types in between. Type B is also considered to be a type A in both relationships. For the complete list of Painless reference types and their supported methods, see the https://www.elastic.co/guide/en/elasticsearch/reference/current/painless-api-reference.html[Painless API Reference]. For more information about working with reference types, see <> and <>. *Examples:* [source,Java] ---- ArrayList al = new ArrayList(); // Declare variable al as an ArrayList and // set it to a newly allocated ArrayList List l = new ArrayList(); // Declare variable l as a List and set // it to a newly allocated ArrayList, which is // allowed because ArrayList inherits from List Map m; // Declare variable m as a Map and set it // to the default value of null ---- Directly accessing static pieces of a reference type. [source,Java] ---- Integer.MAX_VALUE // a static field access Long.parseLong("123L") // a static function call ---- [[string-type]] ==== String Type A `String` is a specialized reference type that is immutable and does not have to be explicitly allocated. You can directly assign to a `String` without first allocating it with the `new` keyword. (Strings can be allocated with the `new` keyword, but it's not required.) When assigning a value to a `String`, you must enclose the text in single or double quotes. Strings are allocated according to the standard Java Memory Model. The default value for a `String` is `null.` *Examples:* [source,Java] ---- String r = "some text"; // Declare String r and set it to the // String "some text" String s = 'some text'; // Declare String s and set it to the // String 'some text' String t = new String("some text"); // Declare String t and set it to the // String "some text" String u; // Declare String u and set it to the // default value null ---- [[void-type]] ==== void Type The `void` type represents the concept of no type. In Painless, `void` declares that a function has no return value. [[array-type]] ==== Array Type Arrays contain a series of elements of the same type that can be allocated simultaneously. Painless supports both single and multi-dimensional arrays for all types except void (including `def`). You declare an array by specifying a type followed by a series of empty brackets, where each set of brackets represents a dimension. Declared arrays have a default value of `null` and are themselves a reference type. To allocate an array, you use the `new` keyword followed by the type and a set of brackets for each dimension. You can explicitly define the size of each dimension by specifying an expression within the brackets, or initialize each dimension with the desired number of values. The allocated size of each dimension is its permanent size. To initialize an array, specify the values you want to initialize each dimension with as a comma-separated list of expressions enclosed in braces. For example, `new int[] {1, 2, 3}` creates a one-dimensional `int` array with a size of 3 and the values 1, 2, and 3. When you initialize an array, the order of the expressions is maintained. Each expression used as part of the initialization is converted to the array's type. An error occurs if the types do not match. *Grammar:* [source,ANTLR4] ---- declare_array: TYPE ('[' ']')+; array_initialization: 'new' TYPE '[' ']' '{' expression (',' expression) '}' | 'new' TYPE '[' ']' '{' '}'; ---- *Examples:* [source,Java] ---- int[] x = new int[5]; // Declare int array x and assign it a newly // allocated int array with a size of 5 def[][] y = new def[5][5]; // Declare the 2-dimensional def array y and // assign it a newly allocated 2-dimensional // array where both dimensions have a size of 5 int[] x = new int[] {1, 2, 3}; // Declare int array x and set it to an int // array with values 1, 2, 3 and a size of 3 int i = 1; long l = 2L; float f = 3.0F; double d = 4.0; String s = "5"; def[] da = new def[] {i, l, f*d, s}; // Declare def array da and set it to // a def array with a size of 4 and the // values i, l, f*d, and s ---- [[casting]] === Casting Casting is the conversion of one type to another. Implicit casts are casts that occur automatically, such as during an assignment operation. Explicit casts are casts where you use the casting operator to explicitly convert one type to another. This is necessary during operations where the cast cannot be inferred. To cast to a new type, precede the expression by the new type enclosed in parentheses, for example `(int)x`. The following sections specify the implicit casts that can be performed and the explicit casts that are allowed. The only other permitted cast is casting a single character `String` to a `char`. *Grammar:* [source,ANTLR4] ---- cast: '(' TYPE ')' expression ---- [[numeric-casting]] ==== Numeric Casting The following table shows the allowed implicit and explicit casts between numeric types. Read the table by row. To find out if you need to explicitly cast from type A to type B, find the row for type A and scan across to the column for type B. IMPORTANT: Explicit casts between numeric types can result in some data loss. A smaller numeric type cannot necessarily accommodate the value from a larger numeric type. You might also lose precision when casting from integer types to floating point types. |==== | | byte | short | char | int | long | float | double | byte | | implicit | implicit | implicit | implicit | implicit | implicit | short | explicit | | explicit | implicit | implicit | implicit | implicit | char | explicit | explicit | | implicit | implicit | implicit | implicit | int | explicit | explicit | explicit | | implicit | implicit | implicit | long | explicit | explicit | explicit | explicit | | implicit | implicit | float | explicit | explicit | explicit | explicit | explicit | | implicit | float | explicit | explicit | explicit | explicit | explicit | explicit | |==== Example(s) [source,Java] ---- int a = 1; // Declare int variable a and set it to the literal // value 1 long b = a; // Declare long variable b and set it to int variable // a with an implicit cast to convert from int to long short c = (short)b; // Declare short variable c, explicitly cast b to a // short, and assign b to c byte d = a; // ERROR: Casting an int to a byte requires an explicit // cast double e = (double)a; // Explicitly cast int variable a to a double and assign // it to the double variable e. The explicit cast is // allowed, but it is not necessary. ---- [[reference-casting]] ==== Reference Casting A reference type can be implicitly cast to another reference type as long as the type being cast _from_ is a descendant of the type being cast _to_. A reference type can be explicitly cast _to_ if the type being cast to is a descendant of the type being cast _from_. *Examples:* [source,Java] ---- List x; // Declare List variable x ArrayList y = new ArrayList(); // Declare ArrayList variable y and assign it a // newly allocated ArrayList [1] x = y; // Assign Arraylist y to List x using an // implicit cast y = (ArrayList)x; // Explicitly cast List x to an ArrayList and // assign it to ArrayList y x = (List)y; // Set List x to ArrayList y using an explicit // cast (the explicit cast is not necessary) y = x; // ERROR: List x cannot be implicitly cast to // an ArrayList, an explicit cast is required Map m = y; // ERROR: Cannot implicitly or explicitly cast [2] // an ArrayList to a Map, no relationship // exists between the two types. ---- [1] `ArrayList` is a descendant of the `List` type. [2] `Map` is unrelated to the `List` and `ArrayList` types. [[def-type-casting]] ==== def Type Casting All primitive and reference types can always be implicitly cast to `def`. While it is possible to explicitly cast to `def`, it is not necessary. However, it is not always possible to implicitly cast a `def` to other primitive and reference types. An explicit cast is required if an explicit cast would normally be required between the non-def types. *Examples:* [source,Java] ---- def x; // Declare def variable x and set it to null x = 3; // Set the def variable x to the literal 3 with an implicit // cast from int to def double a = x; // Declare double variable y and set it to def variable x, // which contains a double int b = x; // ERROR: Results in a run-time error because an explicit cast is // required to cast from a double to an int int c = (int)x; // Declare int variable c, explicitly cast def variable x to an // int, and assign x to c ---- [[boxing-unboxing]] ==== Boxing and Unboxing Boxing is where a cast is used to convert a primitive type to its corresponding reference type. Unboxing is the reverse, converting a reference type to the corresponding primitive type. There are two places Painless performs implicit boxing and unboxing: * When you call methods, Painless automatically boxes and unboxes arguments so you can specify either primitive types or their corresponding reference types. * When you use the `def` type, Painless automatically boxes and unboxes as needed when converting to and from `def`. The casting operator does not support any way to explicitly box a primitive type or unbox a reference type. If a primitive type needs to be converted to a reference type, the Painless reference type API supports methods that can do that. However, under normal circumstances this should not be necessary. *Examples:* [source,Java] ---- Integer x = 1; // ERROR: not a legal implicit cast Integer y = (Integer)1; // ERROR: not a legal explicit cast int a = new Integer(1); // ERROR: not a legal implicit cast int b = (int)new Integer(1); // ERROR: not a legal explicit cast ---- [[promotion]] ==== Promotion Promotion is where certain operations require types to be either a minimum numerical type or for two (or more) types to be equivalent. The documentation for each operation that has these requirements includes promotion tables that describe how this is handled. When an operation promotes a type or types, the resultant type of the operation is the promoted type. Types can be promoted to def at compile-time; however, at run-time, the resultant type will be the promotion of the types the `def` is representing. *Examples:* [source,Java] ---- 2 + 2.0 // Add the literal int 2 and the literal double 2.0. The literal // 2 is promoted to a double and the resulting value is a double. def x = 1; // Declare def variable x and set it to the literal int 1 through // an implicit cast x + 2.0F // Add def variable x and the literal float 2.0. // At compile-time the types are promoted to def. // At run-time the types are promoted to float. ----