Functor in TypeScript

Question

How can I create functor in TypeScript?

EDIT:

Functor is, in C++ world, function that can hold state - basically class that has overriden () operator.

So, for example, I'm able to do following:

class myClass {
    var value : string;
    // how?
    functor() : string {
        return value;
    }
}



var a = new myClass();
a.value = "abc";
a(); // to return "abc"

Answer 1

So really what you have here is a method on a class, like this:

class myClass {
    constructor(private text: string) {

    }

    methodName() : string {
         return this.text;
    }
}

var a = new myClass('Example');
a.methodName(); // 'Example'

If you just want a plain function, you can do that too:

function functor(text : string) : string {
     return "abc";
}

functor('text');

Difference Between JS-Style Functor and Class Output

You can attempt to reproduce a functor, like this:

function functor(text : string) : () => string {
     return function() {
         return text;
     }
}

var x = functor('Example');
x(); // returns 'Example'

But actually, using a class gives you the very similar:

var myClass = (function () {
    function myClass(text) {
        this.text = text;
    }
    myClass.prototype.methodName = function () {
        return this.text;
    };
    return myClass;
})();
var a = new myClass('Example');
a.methodName(); // 'Example'

With the benefits of class semantics... you can extend the class, you can generate an interface from the class and so on.