Has anyone written an

apply

method on iOS that’s behaving similar to Kotlin’s apply?

As in a Swift extension?

Yeah

I’ve never been able to figure out a good way to do it. You can’t add extensions to

Any

or

AnyObject

. You can do something like this:

protocol Applier {
    associatedtype Applying
    func apply(_ fn: (Applying) -> Void) -> Applying
}

extension Applier {
    func apply(_ fn: (Applying) -> Void) -> Applying{
        fn(self as! Self.Applying)
        return self as! Self.Applying
    }
}

class Foo {
    var bar = "baz"
}

extension Foo: Applier {
    typealias Applying = Foo
}


let foo = Foo().apply { `self` in
    self.bar = "baz2"
}

print(foo.bar)

class Foo2: Foo {
    var baz = "foo"
}

let foo2 = Foo2().apply { `self` in
    self.bar = "baz2"
    //self.baz = "Does not work.  Self is of type Foo"
}

It isn’t very useful though as you have to declare the conformance of the type to the

Applier

protocol for each class you want to use it on. The other caveat is the subclass issue. If you make

UIView

conform to the protocol and try to use it on a subclass such as

UILabel

, the type of the argument passed into your apply function is

UIView

which is only minimally useful. Also there should be a way to do the above without the force casts. I’m just too tired to parse through all of the protocol associated type nuances right now.

Argh. That

apply

looks really distasteful. That

let

function should come handy though, thanks

Yeah, I don’t use it nor recommend it. I did ask on Stackoverflow how to improve it. Maybe someone there has an idea. https://stackoverflow.com/questions/61259143/implementing-kotlin-apply-function-in-swift

That’s neat