Customized literals in ECMAScript 4

One neat little feature that has come up in the design of ECMAScript Edition 4 is the ability to define conversions between datatypes. Class-based OO is nice for some purposes, and is certainly popular, but the ability to use syntactic literals to construct data is nice, and usually disappears when you "upgrade" to a bondage-and-discipline language like Java.

In ES4, it looks like you'll be able to define a sort of customized literal syntax for any class by means of an automatic conversion method. For example, imagine the following code:

var kleinBlue : Color = [ 0x00, 0x2F, 0xA7 ]
...
kleinBlue.toCMYK()
...

We can define a Color class with whatever methods we want (such as toCMYK) while still constructing one with a simple, lightweight array literal syntax.

We achieve this by defining a conversion method on the Color class:

class Color {
    ...
    type RGB = [ UInt, UInt, UInt ]
    function to(triple : RGB) {
        type switch (triple) {
            case ([ r, g, b ] : RGB) {
                return new Color(...)
            }
        }
    }
}

Now any context expecting the type Color can also accept an RGB triple and automatically convert it to an instance of Color.