Open Radar

 
Summary:
I’m composing the first function from Swift‘s stdlib with == over T? using a left-to-right composition operator, >>>. When I call it, it crashes if its second operand is typed as Int but not if it’s typed as Int?, but both compile just fine *and* both work when defined manually.


Steps to Reproduce:
Run this:
infix operator >>> {}
public func >>> <T, U, V, W> (f: T -> U, g: (U, V) -> W) -> (T, V) -> W {
	return { g(f($0), $1) }
}

let array = [1, 2, 3]

let manualOptional: ([Int], Int?) -> Bool = { (==)(first($0), $1) }
if manualOptional(array, 1) {
	println("manual optional")
}

let manualNonOptional: ([Int], Int) -> Bool = { (==)(first($0), $1) }
if manualNonOptional(array, 1) {
	println("manual nonoptional")
}

let composedOptional: ([Int], Int?) -> Bool = (first >>> (==))
if composedOptional(array, 1) {
	println("composed optional")
}

let composedNonOptional: ([Int], Int) -> Bool = (first >>> (==))
if composedNonOptional([1, 2, 3], 1) {
	println("composed nonoptional")
}


Expected Results:
I expected it to print all four strings.


Actual Results:
It prints the first three, and then crashes.


Regression:
N/A


Notes:
Crash log attached.