operator-overloading.js

// Stolen from https://github.com/rauschma/op_overload and ported to ES6

const log = console.log.bind(console)

var operands = []

class Point {
	constructor(x, y) {
		if (arguments.length === 0) {
			x = 0
			y = 0
		} else if (arguments.length !== 2) {
			throw new Error("Need either 0 or 2 arguments")
		}
		this.x = x
		this.y = y
	}
	toString = function() {
		return "Point(" + this.x + ", " + this.y + ")"
	}
	valueOf() {
		operands.push(this)
		// Lowest natural number x where the following are all different:
		// x + x, x - x, x * x, x / x
		return 3
	}
	equals = function(other) {
		return this.x === other.x && this.y === other.y
	}
	set _(value) {
		var operator
		if (operands.length >= 2 && value === 3 * operands.length) {
			// 3 + 3 + 3 + ...
			operator = this.setAdd
		} else {
			throw new Error("Unsupported operation (code " + value + ")")
		}
		Point.operands = [] // reset
		return operator.apply(this, operands)
	}
	setAdd(firstOperand) {
		this.x = firstOperand.x
		this.y = firstOperand.y
		;[...arguments].slice(1).forEach(function(op) {
			log(`op is ${op}`)
			this.x += op.x
			this.y += op.y
		}, this)
		return this
	}
	/**
	 * "" + mypoint won't invoke toString(), but valueOf().
	 * Work-around: "" + mypoint._
	 */
	get _() {
		return this.toString()
	}
}

var p = new Point()

p._ = new Point(1, 2) + new Point(3, 4) + new Point(5, 6)
log(p.toString()) // Point(9, 12)