passing an object (self) into extension

Question

I'm experimenting with writing Swifts .filter function and have run into some confusion. I'm essentially trying to modify this function:

func anotherFilter<T>(elements: [T], predicate: (T) -> Bool) -> [T] {
    var filteredArray = [T]()
    for element in elements {
        if predicate(element) {
            filteredArray += [element]
        }
    }
    return filteredArray
}

Into an extension:

extension Array {
    func anotherFilter<T>(elements: [T], predicate: (T) -> Bool) -> [T] {
        var filteredArray = [T]()
        for element in elements {
            if predicate(element) {
                filteredArray += [element]
            }
        }
        return filteredArray
    }
}

Of course this version of the extension works but it requires that you pass the object in which doesn't make sense:

self.coords.anotherFilter (coords) { self.someOperation(coords, op: $0) }

What I've Tried

Obviously, what I'd like to achieve is something like this:

extension Array {

    func anotherFilter <T>(predicate: (T) -> Bool) -> [T] {
        var filteredArray = [T]()
        for item in self {
            if predicate(item) {
                filteredArray.append(item)
            }
        }
    }
}

But this returns an error:

Cannot invoke 'predicate' with an argument list of type '(Element)'

Question

How do I pass the object (in this case coords) into my extension without parameterizing it? Deeper explanations are most welcome.

@MartinR Thanks, i'll take a look. – Dan Beaulieu Nov 29 '15 at 17:18 — Dan Beaulieu, Nov 29 '15 at 17:18

score 1 · Accepted Answer · edited Nov 30 '15 at 20:24

1

Array already has a placeholder type for its elements: Element. Your generic parameter T is exactly that placeholder type, so you can just use Element:

extension Array {
    func anotherFilter(predicate: (Element) -> Bool) -> [Element] {
        var filteredArray = [Element]()
        for item in self where predicate(item) {
            filteredArray.append(item)
        }
        return filteredArray
    }
}

edited Nov 30 '15 at 20:24

Siyual

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answered Nov 29 '15 at 17:13

Nikolai Ruhe

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I just arrived at this a moment ago. Thank you kindly. – Dan Beaulieu Nov 29 '15 at 17:14

score 0 · Answer 2 · answered Nov 29 '15 at 17:09

0

It requires a "self" if the object is not instantiated. I guess it would need to be a static method instead.

static func anotherFilter<T>(elements: [T], predicate: (T) -> Bool) -> [T]

answered Nov 29 '15 at 17:09

Armin

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I'm trying to do away with passing elements: [T] into my extension. – Dan Beaulieu Nov 29 '15 at 17:10

passing an object (self) into extension

Question

2 Answers2