[RESOLVED] using predefined strings to assign to private members possible?

[johanafm]

The part of the code I want help with is in the last part, starting with
for (x in index) {
The rest of the code is a minimized reference for clarification purposes.

The question is wether I can use x to assign to private members. this[x] assigns to public members

/**
 * @param pd string planet data
 */
function Planet(pd) {
	var name, maxpop, type, notes, owner, pop, factories, bases, stargate;
	/**
	 * @member index contains indices into the pd string
	 */
	var index = {
		'name'	: {
			'start'	: 0,
			'end': 10
		},
		'maxpop'	: {
			'start'	: 30,
			'end'	: 31
		},
		'type'	: {
			'start'	: 32,
			'end'	: 33
		},
		'etc' : {}
	}

/* privileged functions */
this.getName = function() { return name; }
/* If I used this.maxpop here, I could use this[x] below. But then the members are
 * also publicly accessible which they shouldn't be
 */
this.getMaxPop = function() { return maxpop; }
/* etc */

/* private functions */
function reverseByte(val) {
	var total = 0;
	for (var i = 0; i < val.length; ++i) {
		total += parseInt(val.charCodeAt(i)) * Math.pow(256, (val.length - 1) - i);
	}
	return total;
}

/*
 *	Is it possible to use the object property names from the "index" member above
 *	to assign to private members name, maxpop etc?
 *
 * using this[x] assigns to public members name, maxpop etc. That is, when x is "maxpop",
 * this[x] will not assign to the private member maxpop.
 *
 * And doing it the way I've done below seems cumbersome.
 */
for (x in index) {
	if (x == 'name') {
		name = pd.substring(index[x].start, index[x].end);
	}
	else {
		switch(x) {
			case 'maxpop':
				maxpop = reverseByte(pd.substring(index[x].start, index[x].end));
				break;
			case 'type':
				type = reverseByte(pd.substring(index[x].start, index[x].end));
				break;
			case 'etc':
				...;
				break;
		}
	}
}
}

[dalecosp]

Gee, I hope you've asked this someplace else. Aren't you the JS guru around here? 😉

[Weedpacket]

A set of accessor functions of some sort?

function Planet() {
...
    this.set = {maxpop: function(val) { maxpop = val; }};
    this.get = {maxpop: function(){return maxpop;}};
...
}


planetInstance.set.maxpop(42);
var foo = planetInstance.get.maxpop();
planetInstance.set['maxpop'](17);

[johanafm]

dalecosp;11025715 wrote:

Gee, I hope you've asked this someplace else. Aren't you the JS guru around here? 😉

Well, I started this little project to learn (more) javascript 🙂

I was actually certain that Weedpacket would have an answer to this... And voilà 🙂

Weedpacket;11025721 wrote:

A set of accessor functions of some sort?

function Planet() {
    this.set = {maxpop: function(val) { maxpop = val; }};

Brilliant. A setter object handles this perfectly. And also, the same technique made it possible to do away with the conditional branch to call either getNullTerminated when setting Planet.name and reverseByte for the others!

Thanks 🙂

For reference, it now looks like this

	var indices = {
		'name'	: {
			'start'	: 0,
			'end'	: 12,
			'extractor'	: getNullTerminated
		},
		'maxpop'	: {
			'start'	: 30,
			'end'	: 31,
			'extractor'	: reverseByte
		},
		etc : {}
	}

this.set = {
	name	: function (v) { name = v; },
	maxpop	: function (v) { maxpop = v; },
	etc : {}
}

// this.set[x] => this.set.name, this.set.maxpop
// and now also calling indices[x].exctractor for indices.name.getNullTerminated(), indices.maxpop.reverseByte()
for (x in index) {
	this.set[x](indices[x].extractor(pd.substring(index[x].start, index[x].end)));
}

And while it may perhaps initially look as if it's an equal amount of typing to get those setter functions in place as typing it out explicitly... First off, I need those setters anyway. Besides, now I can do away with the former setter functions which could not be called the way I needed them: Planet.setName(), Planet.setMaxPop() etc.

[dalecosp]

johanafm;11025737 wrote:

Well, I started this little project to learn (more) javascript 🙂

Bully for you! +1 for personal growth 🙂

I was actually certain that Weedpacket would have an answer to this... And voilà 🙂

Lol, no kidding. I just guess I don't assume he'll answer everything.

Mr. Packet ... assuming there's a bonus this month (I heard rumors) ... do you have an Amazon wishlist? You're too many TZ's away for the lunch/beer/pizza thing ... 😉

[Weedpacket]

Just as a follow-up, I recall that JavaScript does now have support for getter/setter properties (subject to availability in client engines).

get maxpop () {
  return this.privateMaxpop;
}
....
var t1 = o.maxpop;
var t2 = o['maxpop'];

[johanafm]

Thanks for the additional info Weedpacket. But I end up with another couple of questions. I'm starting a new topic for it though, since it's moving off from this one.