[swift-users] Type of expression is ambiguous for static tuples

[Adrian Zubarev]

Yet this is correct behavior because the compiler cannot traverse the expression tree without knowing the root type of that expression tree. The type information flow in such case should be from root to the leaves where the root is NOT the root of the expression, but the type from the function parameter, which then should be passed to the expression tree. However the expression tree is not complete, because there MIGHT be another `phythagoreanTruple` somewhere else. Even if there is no other `phythagoreanTruple`, here the general rules are applied which results into the mentioned error message.

Please correct me if I’m wrong here.


Am 1. September 2017 um 14:53:35, David Hart (david at hartbit.com) schrieb:

Its slightly different though. In the case of:

let cgColor: CGColor = .clear.cgColor

clear is a static property on UIColor, not CGColor. In his example, pythagoreanTriple is a property on Double so it does feel like a bug.

On 1 Sep 2017, at 13:31, Adrian Zubarev via swift-users <swift-users at swift.org> wrote:

It’s because the compiler does not support this yet. It’s the same with `let cgColor: CGColor = .clear.cgColor // will not work`.

Instead you need to write `UIColor.clear.cgColor` or in your case `Double.phythagoreanTruple.0`


Am 1. September 2017 um 12:17:57, Rudolf Adamkovič via swift-users (swift-users at swift.org) schrieb:

Given the following extension ...

extension Double {
    typealias Triple = (Double, Double, Double)
    static let pythagoreanTriple: Triple = (3, 4, 5)
}
... why does Swift compiler emits the following errors?

// Type of expression is ambiguous without more context
let a: Double = .pythagoreanTriple.0

// Type of expression is ambiguous without more context
func f(_ x: Double) {}
f(.pythagoreanTriple.0)
The errors disappear with explicit Double.pythagoreanTriple.0.

Why doesn't the compiler infer Double in this case?

FYI: Posted also to Stack Overflow here:

https://stackoverflow.com/questions/45998034/type-of-expression-is-ambiguous-for-static-tuples

R+

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