Given this mocked example:

Pretend this is in the Swift Standard Library

enum StandardThing {
    case value
}
extension Foo {
    func doSomething(_ t: StandardThing) {...}
}

And this is in my own code

enum TotallyOtherThing {
    case value
}
extension Foo {
    func doSomething(_ t: TotallyOtherThing) {...}
}

I can call doSomething(_:) and pass in either StandardThing.value or TotallyOtherThing.value. If I pass in only .value, the compiler is still happy, and defaults to using my overload instead of the standard library version. My question is around the precedence of this. Is an external overload always prioritized over standard library implementations, given equivalent specificity of the params? Or is this a coincidence and could change in the future?