#29: Interesting Uses of @autoclosure

@autoclosure wraps an expression in a closure automatically. It is useful when you want a convenient API but you still want the argument to be evaluated lazily.

A classic example is logging only when needed:

func debugLog(_ message: @autoclosure () -> String) {
    #if DEBUG
    print(message())
    #endif
}

debugLog(expensiveDebugDescription())

If DEBUG is off, the expensive expression is never evaluated.

Use @autoclosure sparingly. It can make APIs pleasant, but it also hides the fact that a closure is involved, so it is best reserved for small helper functions where the behavior is obvious.