[GROOVY-6488] Closure to SAM coercion cannot infer generic return type

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.2.1
• Fix Version/s: 2.2.2
• Component/s: Static compilation
• Assignee: Cédric Champeau
• Reporter: Luke Daley
• Created: 15/Dec/13 09:04
• Updated: 04/Mar/14 16:31
• Resolved: 21/Jan/14 14:46

Description

Given the following:

import groovy.transform.CompileStatic

import java.util.concurrent.Callable

interface CustomCallable<T> {
  T call()
}

class Thing {
  static <T> T customType(CustomCallable<T> callable) {
    callable.call()
  }

  static <T> T callable(Callable<T> callable) {
    callable.call()
  }

  @CompileStatic
  static void run() {
    callable { [] }.add(1) // return type is inferred - passes compile
    customType { [] }.add(1) // return type is not inferred - fails compile
  }
}

The problem is visible in the run() method above.

It would be extremely useful for typed DSLs if the return type can be inferred for SAM coercion.