Package groovy.transform.stc

Class MapEntryOrKeyValue

java.lang.Object
groovy.transform.stc.ClosureSignatureHint
groovy.transform.stc.MapEntryOrKeyValue
public class MapEntryOrKeyValue
extends ClosureSignatureHint

A special hint which handles a common use case in the Groovy methods that work on maps. In case of an iteration on a list of map entries, you often want the user to be able to work either on a Map.Entry map entry or on a key,value pair.

The result is a closure which can have the following forms:

  • { key, value -> ... } where key is the key of a map entry, and value the corresponding value
  • { entry -> ... } where entry is a Map.Entry map entry
  • { ... } where it is an implicit Map.Entry map entry

This hint handles all those cases by picking the generics from the first argument of the method (by default).

The options array is used to modify the behavior of this hint. Each string in the option array consists of a key=value pair.

  • argNum=index of the parameter representing the map (by default, 0)
  • index=true or false, by default false. If true, then an additional "int" parameter is added, for "withIndex" variants
void doSomething(String str, Map<K,>V map, @ClosureParams(value=MapEntryOrKeyValue.class,options="argNum=1") Closure c) { ... }

  • Constructor Details

    • MapEntryOrKeyValue

      public MapEntryOrKeyValue()

  • Method Details

    • getClosureSignatures

      public List<ClassNode[]> getClosureSignatures​(MethodNode node, SourceUnit sourceUnit, CompilationUnit compilationUnit, String[] options, ASTNode usage)
      Description copied from class: ClosureSignatureHint

      Subclasses should implement this method, which returns the list of accepted closure signatures.

      The compiler will call this method each time, in a source file, a method call using a closure literal is encountered and that the target method has the corresponding Closure parameter annotated with ClosureParams. So imagine the following code needs to be compiled:

      @groovy.transform.TypeChecked void doSomething() { println ['a','b'].collect { it.toUpperCase() } }

      The collect method accepts a closure, but normally, the type checker doesn't have enough type information in the sole DefaultGroovyMethods.collect(java.lang.Iterable, groovy.lang.Closure) method signature to infer the type of it. With the annotation, it will now try to find an annotation on the closure parameter. If it finds it, then an instance of the hint class is created and the type checker calls it with the following arguments:

      Now, the hint instance can return the list of expected parameters. Here, it would have to say that the collect method accepts a closure for which the only argument is of the type of the first generic type of the first argument.

      With that type information, the type checker can now infer that the type of it is String, because the first argument (here the receiver of the collect method) is a List<String>

      Subclasses are therefore expected to return the signatures according to the available context, which is only the target method and the potential options.

      Specified by:
      getClosureSignatures in class ClosureSignatureHint
      Parameters:
      node - the method node for which a Closure parameter was annotated with ClosureParams
      sourceUnit - the source unit of the file being compiled
      compilationUnit - the compilation unit of the file being compiled
      options - the options, corresponding to the ClosureParams.options() found on the annotation @return a non-null list of signature, where a signature corresponds to an array of class nodes, each of them matching a parameter.
      usage - the AST node, in the compiled file, which triggered a call to this method. Normally only used for logging/error handling