Swift shorthand argument syntax oddities

odd.swift

// The Swift Programming Language book from Apple states the following:
//
// Swift automatically provides shorthand argument names to inline closures, 
// which can be used to refer to the values of the closure’s arguments by the
// names $0, $1, $2, and so on.


// In Xcode 6.1 and 6.2b1, it appears that this is only true IF the last argument
// is referenced using shorthand syntax somewhere in the closure body. See below
// for details.


func test(block: (Int)->Void) {
    block(1)
}
test { println($0) }    // prints "1"

println("\n")

func test2(block: (Int, Int)->Void) {
    block(1, 2)
}
test2 { println($0) }    // prints "(1, 2)"    ????  $0 is the whole tuple???
test2 { println($1) }    // prints "2"
test2 { println($0); $1} // prints "1"         ????  ... but only if other arguments are unused?

println("\n")

func test3(block: (Int, Int, Int)->Void) {
    block(1, 2, 3)
}

test3 { println($0) }  // prints "(1, 2, 3)"   ????  okay, at least we're being consistent
test3 { println($2) }  // prints "3"


test3 { println($1) }  // !!! Does not compile !!!
// error: tuple types '(Int, Int, Int)' and '(($T2, ($T2, $T3) -> ($T2, $T3) -> $T1) -> ($T2, ($T2, $T3) -> $T1) -> $T1, (($T2, $T3) -> ($T2, $T3) -> $T1, $T3) -> (($T2, $T3) -> $T1, $T3) -> $T1)' have a different number of elements (3 vs. 2)