Paul King created GROOVY-12216:
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Summary: Fat-free twins for the fold/reduce DGM methods (inject,
injectAll)
Key: GROOVY-12216
URL: https://issues.apache.org/jira/browse/GROOVY-12216
Project: Groovy
Issue Type: Sub-task
Reporter: Paul King
Assignee: Paul King
h3. Summary
Sub-task of GROOVY-12205. Adds functional-interface twins for the fold/reduce
family. Grouped together because they share one design decision — the
{{BinaryOperator}} vs {{BiFunction}} choice and how it pairs with the
{{initialValue}} overloads — so the type conventions are settled once.
{{inject}} on {{Iterable}} already has both twins (from GROOVY-12054); this
completes the remaining receivers.
({{sum}} was originally grouped here but is split out — its twin collides
positionally with an existing {{Object initialValue}} overload; see the
separate {{sum}} item.)
h3. Type convention
* No-initial-value forms (2-arg reduce): {{BinaryOperator<T>}}.
* Initial-value forms (3-arg reduce): {{BiFunction<? super U, ? super E, ?
extends U>}}, matching the existing {{inject(Iterable, U, BiFunction)}}.
No collision risk: in both methods the reduce function sits in a distinct
trailing position after any explicit {{initialValue}} parameter, so it never
competes with the initial value for overload selection.
h3. Methods
||Method||Closure overloads without a twin||Functional type||Receivers||
|{{inject}}|8|{{BinaryOperator<T>}} (no init) / {{BiFunction<? super U, ? super
E, ? extends U>}} (init)|no-init: Object, {{E[]}}, Collection; with-init:
Object, Iterator, Map, {{E[]}}, Collection|
|{{injectAll}}|5|{{BinaryOperator<T>}} (no init) / {{BiFunction}}
(init)|no-init: Iterable, Iterator; with-init: Iterable, Iterator, Map|
Total: 13 new overloads.
h3. Conventions (per GROOVY-12054)
* PECS wildcards; {{@since 6.0.0}}; inline javadoc example via {{<pre
class="language-groovy groovyTestCase">}} cross-linking the {{Closure}}
counterpart with {{@link}}.
* Plain single-SAM overloads only — not {{@Incubating}}.
h3. Compatibility
* *{{inject}} arity*: since {{BinaryOperator<T> extends BiFunction<T,T,T>}},
the no-init ({{BinaryOperator}}, 2-arg) and with-init ({{BiFunction}}, 3-arg)
forms stay distinct by arity — no erasure clash, mirroring the existing
{{Iterable}} pair.
* Existing closure/lambda call sites unaffected; method references and typed
functional values select the twin under {{@CompileStatic}} (GROOVY-12214). Only
check: an existing {{@CompileStatic}} call passing a literal {{null}} to a
currently-single-overload form would become ambiguous — grep-checkable,
resolved with a cast if found.
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