How to call ambiguous method?

Question

given this code

extension Array {
    func filter(includeElement: (T) -> Bool) -> T[] {
        var ret = T[]()
        for e in self {
            if includeElement(e) {
                ret += e
            }
        }
        return ret
    }
}

var a = [1,2]
var b = a.filter() {i in print(i); return true}

it can't compile with error message

error: ambiguous use of 'filter'
var b = a.filter() {i in print(i); return true}
        ^
Swift.Array<T>:84:8: note: found this candidate
  func filter(includeElement: (T) -> Bool) -> Array<T>
       ^
<REPL>:30:10: note: found this candidate
    func filter(includeElement: (T) -> Bool) -> T[] {
         ^

so looks like I am allowed to create extension method with duplicated method and signature, but I somehow need a special way to call it

---

BTW, default Array.filter is broken, it calls the closure twice for each element and crashes REPL or give your rubbish result in playground if the result is inconsistent

xiliangchen-imac:~ xiliangchen$ xcrun swift
Welcome to Swift!  Type :help for assistance.
  1> let arr = [1,2,3,4,5]
arr: Int[] = size=5 {
  [0] = 1
  [1] = 2
  [2] = 3
  [3] = 4
  [4] = 5
}
  2> var i = 0
i: Int = 0
  3> let arr2 = arr.filter() {
  4.         println($0)
  5.         return i++ < 5
  6. }   
Segmentation fault: 11

Answer 1

There is no problem with defining ambiguous methods, I think. The problem arises when you import 2 ambiguos methods from different modules. Unfortunately, there is no way how to exclude the Array.filter from being imported.

I did some tests and it appears to me the behavior for ambigious definitions is not well defined, for example:

extension NSString {
    func hasPrefix(aString: String!) -> Bool {
        return false
    }
}

let string: NSString = "test"

var hasPrefix = string.hasPrefix("t")
println("Has prefix: \(hasPrefix)") //prints "true"

var method = string.hasPrefix
hasPrefix = method("t")

println("Has prefix: \(hasPrefix)") //prints "false"

The behavior could be different for obj-c classes...

For functions, it appears the definition from current module is preferred:

func NSStringFromCGPoint(point: CGPoint) -> String! {
    return "My method"
}

var point = CGPoint(x: 10.0, y: 10.0)

println("Point: \(NSStringFromCGPoint(point))") //Prints "My method"
println("Point: \(UIKit.NSStringFromCGPoint(point))") //Prints "{10, 10}"