How to give groovy closure parameter a type

Question

I know closures have implicit type 'it' such that we can define a function

def int foo(int num, Closure closure){
  def sum = num
   sum+=closure.call(1)
}

then i call this function like

def total = foo(1,{it+1})
print total
//prints 2

My question is how do i force the closure to take an explicit parameter of type int. Like how we can define lambda functions in java.

Answer 1

You can use @ClosureParam to annotate your Closure argument declaration with its parameters specifications. In your particular case:

import groovy.transform.stc.ClosureParams
import groovy.transform.stc.FirstParam

int foo(int num, @ClosureParams(FirstParam) Closure closure) {
    def sum = num
    sum += closure.call(5)
}

where FirstParam is a hint that says that the argument of closure is of type equals as the first parameter of this method.

Complete code on GitHub

Hope this helps.