Rxswift: Custom filters

[gregpardo]

This isn't really a bug but more of a question. I'm trying to implement some custom filters and I'm not sure where I'm going wrong.

public extension ObservableType {
    @warn_unused_result(message="http://git.io/rxs.uo")
    public func notNil() -> Observable<E> {
        return self.filter { $0 != nil }
    }
}

public extension ObservableType where E == String {
    @warn_unused_result(message="http://git.io/rxs.uo")
    public func notEmpty() -> Observable<E> {
        return self.filter { $0.characters.count > 0 }
    }
}

The goal is to be able to write

someObservable
    .notNil()
    .subscribe

Instead of

someObservable
    .filter { $0 != nil }
    .subscribe

It's really not a huge deal to just write filter but I figured I'd ask since I'm missing something here.

[kzaher]

Hi,

I think that compiler doesn't know

public extension ObservableType where E: OptionalType { // <-- you have to create and implement OptionalType and make Optional conform to it
    @warn_unused_result(message="http://git.io/rxs.uo")
    public func notNil() -> Observable<E> {
        return self.filter { $0.hasValue }
    }
}

... that E is comparable with nil, so there are ways to tell him that (creating an protocol OptionalType and conforming Optional to it).

[gregpardo]

Thanks! This seems to be working.

public protocol OptionalType {
    func hasValue() -> Bool
}

extension Optional: OptionalType {
    public func hasValue() -> Bool {
        return (self != nil)
    }
}

public extension ObservableType where E: OptionalType {
    @warn_unused_result(message="http://git.io/rxs.uo")
    public func notNil() -> Observable<E> {
        return self.filter { $0.hasValue() }
    }
}

public extension ObservableType where E == String {
    @warn_unused_result(message="http://git.io/rxs.uo")
    public func notEmpty() -> Observable<E> {
        return self.filter { $0.characters.count > 0 }
    }
}

[gregpardo]

Closing this out thanks for the help again!

[kzaher]

No problem :)