Swift subscript tricks

CollectionType+subscript.swift

// http://stackoverflow.com/questions/25329186/safe-bounds-checked-array-lookup-in-swift-through-optional-bindings/30593673#30593673

extension CollectionType {
    /// Returns the element at the specified index iff it is within bounds, otherwise nil.
    subscript (safe index: Index) -> Generator.Element? {
        return indices.contains(index) ? self[index] : nil
    }
}

// Usage:
if let element = array[safe: 17] { }