Dynamic method replacement

Evolution Pitches
16

A solution which respects the current language and requirement constraints would look something like this:

class Thing {
    public func theAnswer() -> Int {
        if let replaceableAnswer = Thing.replaceableAnswer {
            return replaceableAnswer(self, self.theAnswerOriginal)
        }
        else
        {
            return theAnswerOriginal()
        }
    }
    
    private func theAnswerOriginal() -> Int {
        return 20
    }
    
    static var replaceableAnswer: ((_ thing: Thing, _ original: () -> Int) -> Int)?
}

let thing = Thing()

print(thing.theAnswer())

Thing.replaceableAnswer = {
    (thing, original) in
    return original() + 22
}

print(thing.theAnswer())

I think this shows just how Allow dynamic keyword on non-objc properties and this pitch is different.

It appears that dynamic has alight been slightly repurposed in Swift by the creation of @dynamicMemberLookup. Maybe replaceable would be a more accurate keyword for this.