Swift Array.filter method

Question

Swift's filter method is defined as follows:

func filter(includeElement: (T) -> Bool) -> [T]

Why does filter definition in Swift's array does not have <T> in its definition (i.e. filter(...))?

I think it's implied. This was mentioned at some point during the generics section of this talk: developer.apple.com/videos/wwdc/2014/#404 — Eran Globen
– Eran Globen, Commented Sep 9, 2014 at 3:29

Antonio · Accepted Answer · 2014-09-09 06:29:20Z

2

filter is a method of the Array<T> class, so T is specified at class level and there is no need to replicate that in the method - actually doing that at method level is a mistake:

struct Array<T> ... {
    func filter<V>(includeElement: (V) -> Bool) -> [V]
}

because V is a different type that has no relationship with T (unless you set constraints in the generic definition). By mistake I mean T and V are different types, whereas it could be thought they are the same. Having a generic class with a generic method is perfectly legit though.

edited Sep 9, 2014 at 6:29

answered Sep 9, 2014 at 5:02

Antonio

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Comments

user4007645 · Accepted Answer · 2014-09-09 05:08:47Z

0

it is because this function is defined in an extension to Array struct and the definition of Array has the in its definition : struct Array

class AA<T> {
}

extension AA {
    func something(aThing: T) -> T{
        return aThing
    }
}

answered Sep 9, 2014 at 5:08

user4007645

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