What is the Swift equivalent of C#/.NET/LINQ's Enumerable.All method?

Question

I want a function that applies a given function to a sequence and returns true iff the given function returns true for every element of the sequence, like Enumerable.All from th

Answer 1

Building up on Jon's answer: You can use contains() instead of an (explicit) loop:

extension SequenceType {
    func all(@noescape predicate: (Self.Generator.Element) throws -> Bool)
        rethrows -> Bool {
            return !(try contains { !(try predicate($0)) })
    }
}

Answer 2

There isn't a built-in function to do this, but you can easily add your own as a protocol extension method:

extension SequenceType {
    func all(@noescape predicate: (Self.Generator.Element) throws -> Bool)
        rethrows -> Bool {

        for i in self {
            if !(try predicate(i)) { return false }
        }
        return true
    }
}

and then use it on a sequence like:

let allPositive = [1, 2, 3].all { $0 > 0 }

Answer 3

Not sure if this helps, but you can achieve the same outcome using reduce. Here's a quick playground I put together to prove the concept:

let nums = [2, 2, 3, 4]

// Will only evaluate to true if all numbers are even.
let allEven = nums.reduce(true) {
    if !$0 || $1 % 2 != 0 {
        return false
    }
    return true
}