C++-style stream output for Swift. (For fun only: Never, ever use this.)

cout.swift

import Foundation

// Swift's << operator is not left-associative, so we'll use <<< instead
operator infix <<< { associativity left }

// Output operator for Streamable objects
func <<< (var outputStream: OutputStream, streamable: Streamable) -> OutputStream {
    // Note: It seems like streamable.writeTo(&outputStream) should work, but playground crashes,
    //       so we write to a string and then output the string
    var outputString = ""
    streamable.writeTo(&outputString)
    outputStream.write(outputString)
    return outputStream
}

// Output operator for Printable objects
func <<< (var outputStream: OutputStream, printable: Printable) -> OutputStream {
    outputStream.write(printable.description)
    return outputStream
}

// Output operator for functions, e.g. endl()
func <<< (var outputStream:OutputStream, f: OutputStream -> OutputStream) -> OutputStream {
    return f(outputStream)
}

// Write newline to a stream
func endl(var outputStream: OutputStream) -> OutputStream {
    outputStream.write("\n")
    return outputStream
}

// Swift Strings are OutputStreams, so no need for a StringBuilder/StringOutputStream
let myString = ""
myString <<< 1 <<< " + " <<< 2 <<< " = " <<< (1 + 2) <<< endl
print(myString)                                                          // "1 + 2 = 3\n"

class ConsoleOutputStream: OutputStream {
    func write(string: String) {
        print(string)
    }
}
let cout = ConsoleOutputStream()
cout <<< "Hello, world!" <<< endl