overloadable_function

overloadable_function.js

function fun(org = function(...args) { throw new Error("overload failed", args.map(a => typeof a)); }, ... others) {
	const overload_functions = {};
	if(others.length) {
		overload_functions[others.map(a => a.constructor.name)] = org;
		org = function(...args) { throw new Error("overload failed", args.map(a => typeof a)); };
	}
	const f = function(... args) {
		return ((overload_functions[args.map(a => a.constructor.name)] || org).bind(this))(... args);
	}
	f.overload = function(overloading_function, ...args) {
		overload_functions[args.map(a => a.constructor.name)] = overloading_function;
		return f;
	};
	return f;
}

class Obj {};
class Other {};

const f = fun()
	.overload(function(p) {
		console.log("A:", p);
	}, 0)
	.overload(function(p, q, r) {
		console.log("B:", p, q, r);
	}, "", 0, new Obj())
	.overload(function(p, q, r) {
		console.log("C:", p, q, r);
	}, "", 0, new Other());

try {
	f();
} catch(e) {
	console.log(e.message);
}

f(4);
f("hoge", 3, new Obj());
f("hoge", 3, new Other());

try {
	f(1, 2, 3);
} catch(e) {
	console.log(e.message);
}

const g = {
	f: fun(function() { console.log(this.name); })
		.overload(function(name) { console.log(this.name, name); }, ""),
	name: "hoge"
};

g.f();
g.f(1, 2, 3);
g.f("fuge");

const h = {
	name: "bar",
	f: g.f,
};

h.f();
h.f("fuge");

class Foo {
	constructor() {
	}
	
	f(p) { console.log("default"); }
};

Foo.prototype.f = fun(Foo.prototype.f, "").overload(function(x) { console.log("number", x); }, 0);

foo = new Foo();
foo.f("");
foo.f(1);