Package groovy.transform

Annotation Interface Associative

@Documented
@Incubating
@Target(METHOD)
@Retention(RUNTIME)
public @interface Associative

Declares that a two-argument combining method is associative: combine(a, combine(b, c)) produces the same result as combine(combine(a, b), c) for all inputs.

Associativity is the contract that makes a combiner safe to use with order-independent reductions such as the parallel Collection methods (sumParallel, injectParallel). Tooling such as groovy.typecheckers.CombinerChecker consumes this declaration to verify, at compile time, that a combiner passed to a parallel reduction carries the contract.

This annotation asserts the law; it does not prove it. The assertion is intended to be backed by tests (for example auto-derived property-based tests). See also Reducer, which additionally declares an identity element.

Since:

6.0.0