Open Radar

 
This appears to be the reason behind this never working:

    var array = [(1, 2), (3, 4)]
    array.append((5, 6))
    // error: missing argument for parameter #2 in call

When generic structs are specialized with a tuple type, methods can't be called with a literal of that instance's specialized type. Those same methods can be called with a tuple variable. Methods that explicitly accept a tuple don't have an issue -- they accept both tuple literals and tuple variables.

Steps to Reproduce:
1. Open Xcode
2. Create a new playground
3. Enter the following code:

struct TestGeneric<T> {
    func goodMethod(arg: (Int, Int)) {
        println(arg)
    }
    
    func badMethod(arg: T) {
        println(arg)
    }
}

var test = TestGeneric<(Int, Int)>()
let tuple = (1, 2)
test.goodMethod(tuple)
test.goodMethod((3, 4))
test.badMethod(tuple)
test.badMethod((3, 4))      // this is the line that fails


Expected Results:
The console should show:

(1, 2)
(3, 4)
(1, 2)
(3, 4)

Actual Results:
The console shows an error message:

Playground execution failed: <EXPR>:38:16: error: missing argument for parameter #2 in call
test.badMethod((3, 4))