Variables

Serverless Stack

Variables are containers for storing data values in your Painless scripts. Variables hold different types of data like numbers, text, lists, and other values that you can access and manipulate throughout your script.

In Painless, every variable must be declared with a specific type before you can use it. This type determines what kind of data the variable can hold and what operations you can perform on it. For example, you might use an int variable to store a document’s score, a String variable to store a field value, or a List variable to collect multiple results.

Painless supports three main categories of variable types:

• Primitive types for basic data such as int, double, boolean, and char. These store simple values directly and have default values (0 for numbers, false for boolean).
• Reference types for complex objects such as String, list, map, and array types like int[]. These store references to objects and default to null when not initialized.
• Dynamic type with def that can represent any type of value, determined at runtime. This provides flexibility when the exact type isn’t known in advance.

Before using a variable, you must declare it with the format type followed by an identifier. If the variable is an array-type, use an opening [ token and a closing ] token for each dimension directly after the identifier. Specify a comma-separated list of identifiers following the type to declare multiple variables in a single statement. Use an assignment operator combined with a declaration to immediately assign a value to a variable. A variable not immediately assigned a value will have a default value assigned implicitly based on the type.

• If a variable is used prior to or without declaration.

declaration : type ID assignment? (',' ID assignment?)*;
type: ID ('.' ID)* ('[' ']')*;
assignment: '=' expression;
		

• Different variations of variable declaration

  int x;
  List y;
  int x, y = 5, z;
  def d;
  int i = 10;
  float[] f;
  Map[][] m;
  		

  1. declare int x; store default null to x
  2. declare List y; store default null to y
  3. declare int x; store default int 0 to x; declare int y; store int 5 to y; declare int z; store defaultint 0 to z;
  4. declare def d; store default null to d
  5. declare int i; store int 10 to i
  6. declare float[] f; store default null to f
  7. declare Map[][] m; store default null to m

Use the assignment operator '=' to store a value in a variable for use in subsequent operations. Any operation that produces a value can be assigned to any variable as long as the types are the same or the resultant type can be implicitly cast to the variable type.

Errors

An error if the type of value is unable to match the type of variable.

Grammar

assignment: ID '=' expression
		

Examples

• Variable assignment with an integer literal

  int i;
  i = 10;
  		

  1. declare int i; store default int 0 to i
  2. store int 10 to i

• Declaration combined with immediate assignment

  int i = 10;
  double j = 2.0;
  		

  1. declare int i; store int 10 to i
  2. declare double j; store double 2.0 to j

• Assignment of one variable to another using primitive type values

  int i = 10;
  int j = i;
  		

  1. declare int i; store int 10 to i
  2. declare int j; load from i → int 10; store int 10 to j

• Assignment with reference types using the new instance operator

  ArrayList l = new ArrayList();
  Map m = new HashMap();
  		

  1. declare ArrayList l; allocate ArrayList instance → ArrayList reference; store ArrayList reference to l
  2. declare Map m; allocate HashMap instance → HashMap reference; implicit cast HashMap reference to Map reference → Map reference; store Map reference to m

• Assignment of one variable to another using reference type values

  List l = new ArrayList();
  List k = l;
  List m;
  m = k;
  		

  1. declare List l; allocate ArrayList instance → ArrayList reference; implicit cast ArrayList reference to List reference → List reference; store List reference to l
  2. declare List k; load from l → List reference; store List reference to k; (note l and k refer to the same instance known as a shallow-copy)
  3. declare List m; store default null to m
  4. load from k → List reference; store List reference to m; (note l, k, and m refer to the same instance)

• Assignment with array type variables using the new array operator.

  int[] ia1;
  ia1 = new int[2];
  ia1[0] = 1;
  int[] ib1 = ia1;
  int[][] ic2 = new int[2][5];
  ic2[1][3] = 2;
  ic2[0] = ia1;
  		

  1. declare int[] ia1; store default null to ia1
  2. allocate 1-d int array instance with length [2] → 1-d int array reference; store 1-d int array reference to ia1
  3. load from ia1 → 1-d int array reference; store int 1 to index [0] of 1-d int array reference
  4. declare int[] ib1; load from ia1 → 1-d int array reference; store 1-d int array reference to ib1; (note ia1 and ib1 refer to the same instance known as a shallow copy)
  5. declare int[][] ic2; allocate 2-d int array instance with length [2, 5] → 2-d int array reference; store 2-d int array reference to ic2
  6. load from ic2 → 2-d int array reference; store int 2 to index [1, 3] of 2-d int array reference
  7. load from ia1 → 1-d int array reference; load from ic2 → 2-d int array reference; store 1-d int array reference to index [0] of 2-d int array reference; (note ia1, ib1, and index [0] of ia2 refer to the same instance)