Open Radar

 
Summary:
In some contexts, argument lists are automatically promoted to tuples by the compiler. However this behaviour is inconsistent.

The following example demonstrates this issue:

var array: [(Int, Int)] = []
var int_var = 1
let int_let = 1


// This works
array.append(int_let, int_let)

// "Cannot invoke 'append' with an argument list of type '(Int, Int)'"
array.append(int_let, 1)

// "Cannot invoke 'append' with an argument list of type '(Int, Int)'"
array.append(1, 1)

// "Cannot invoke 'append' with an argument list of type '(Int, Int)'"
array.append(int_var, 1)

// "Cannot invoke 'append' with an argument list of type '(Int, Int)'"
array.append(int_var, int_var)


// These work
array.append((int_let, 1))
array.append((1, 1))
array.append((int_var, 1))
array.append((int_var, int_var))


An Xcode project demonstrating this issue is also attached.

Steps to Reproduce:
Open the attached project and you should see the compiler errors.

Expected Results:
Either no automatic promotion to tuples should occur, meaning

array.append(int_let, int_let)

should also produce an error, or tuple promotion should work consistently for all the given examples, meaning the given program should compile without errors.

Actual Results:
Tuple promotion is inconsistent, working only in one of the provided examples.

Version:
Xcode 7.1b3 (7B85)
Apple Swift version 2.1 (swiftlang-700.1.101.3 clang-700.1.75)
OS X 10.11 (15A284)