Provides failable initializers for X-Literals, e.g., `String(suspectedString) // returns a String optional`, just like `String(5) // returns a String, "5"`

OptionalLiteralType.swift

/*
Instead of, say:

    if let definitelyAString = perhapsAString as? String { // yadda... }

We now have:

    String(perhapsAString) // returns a String? (an optional)
 */
protocol OptionalLiteralType {
    init?(_ input: Any?)
}

// The magic, brought to you by Default Protocol Implementations
// cf. The Swift Programming Language p.533
extension OptionalLiteralType {
    init?(_ input: Any?) {
        guard let typedValue = input as? Self else { return nil }
        self = typedValue
    }
}

extension StringLiteralType: OptionalLiteralType {}
extension FloatLiteralType: OptionalLiteralType {}
extension IntegerLiteralType: OptionalLiteralType {}

Provides failable initializers for X-Literals, e.g.,

String(suspectedString) // returns a String optional,

just like

String(5) // returns a String, "5"