[GROOVY-5743] Typed closure as a default parameter requires cast when method is TypeChecked - ASF JIRA

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If you have a typed Closure as a default parameter of a method ie:

@groovy.transform.TypeChecked
Integer a( String s, Closure<Integer> b={ String it -> it.length() } ) {
  b( s )
}

a( 'tim' )

You get the exception:

[Static type checking] - Cannot return value of type java.lang.Object on method returning type java.lang.Integer -> java.lang.Integer

The workaround is to either cast the return:

  (Integer)b( s )

Or stop using the default parameter:

@groovy.transform.TypeChecked
Integer a( String s ) {
  Closure<Integer> b={ String it -> it.length() }
  b( s )
}

a( 'tim' )