Swift: how can String.join() work custom types?

Question

for example:

var a = [1, 2, 3]    // Ints
var s = \",\".join(a)  // EXC_BAD_ACCESS

Is it possible to make the join function return \"1,2,3\

Answer 1

A Swift 3 solution

public extension Sequence where Iterator.Element: CustomStringConvertible {
    func joined(seperator: String) -> String {
        return self.map({ (val) -> String in
            "\(val)"
        }).joined(separator: seperator)
    }
}