@Incubating
class CombinerChecker
extends TypeCheckingDSL

A compile-time checker that verifies the combiner passed to an order-independent parallel reduction (sumParallel, injectParallel) carries the associativity contract those methods silently require — mirroring the design of PurityChecker.

Associativity is undecidable in general, so this checker is deliberately conservative. It has two modes, selected via the extension option mode:

 // default (lenient): only flag high-confidence problems
 @TypeChecked(extensions = 'groovy.typecheckers.CombinerChecker')

 // strict: additionally require the combiner to be declared @Associative/@Reducer
 @TypeChecked(extensions = "groovy.typecheckers.CombinerChecker(mode: 'strict')")
 

What it does, by combiner shape:

• Method reference to a method annotated Associative or Reducer — accepted.
• Inline closure whose combine expression applies a non-associative operator (-, /, %, **) directly to the two combiner parameters (e.g. { a, b -> a - b }) — flagged in any mode (high confidence).
• injectParallel seed that contradicts a @Reducer's declared zero() (both statically constant) — flagged.
• Un-annotated method references and other inline closures — flagged only in strict mode (a declared, verifiable contract is required).

Since:

6.0.0

See Also:

Associative

Reducer