Class FromAbstractTypeMethods

  • public class FromAbstractTypeMethods
    extends ClosureSignatureHint
    This signature hint uses abstract methods from some type (abstract class or interface) in order to infer the expected parameter types. This is especially useful for closure parameter type inference when implicit closure coercion is in action.
    • Constructor Detail

      • FromAbstractTypeMethods

        public FromAbstractTypeMethods()
    • Method Detail

      • 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.util.Collection, 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
        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