Fwd: ||= is much needed?

[Rick Waldron]

This message seems to have disappeared from the archive and since I
referred to it in
http://wiki.ecmascript.org/doku.php?id=strawman:default_operator I wanted
to make sure a record existed.

Rick

---------- Forwarded message ----------
From: Ryan Florence <rpflorence at gmail.com>
Date: Tue, Jun 12, 2012 at 11:45 AM
Subject: Re: ||= is much needed?
To: Rick Waldron <waldron.rick at gmail.com>
Cc: David Bruant <bruant.d at gmail.com>, es-discuss at mozilla.org


I use ||= very regularly in ruby and coffeescript, both of which have
default arguments.

 I definitely agree that default arguments are a decent alternative. I
> can't recall examples where it wouldn't be enough. Do you have use cases
> where you would use ||= and default argument values couldn't be used?
>

Its super handy for caching and late/dynamic initialization of object
properties.


var events = {

  _callbacks: {},

  on: function (topic, callback) {
    (this._callbacks[topic] ||= []).push(callback);
    ...
  },
  ...
};


It's also useful for settings object defaults, especially for expensive
settings that you don't want to calculate in some `defaults` object that is
merged into the settings.

function ajaxWithError (settings) {
  settings.method ||= 'POST';

  settings.elementPosition ||= this._getElementPositions();

  settings.somethingWithInitialization ||= (function(){
    var thing = new Thing();
    thing.foo = settings.foo;
    return thing;
  })();
  ...
};


The ||= (function(){})() should remind any rubyist of `||= begin ... end`
which is beloved by many.

So yeah, I think its really useful outside of default arguments.

- Ryan Florence


On Jun 12, 2012, at 9:06 AM, Rick Waldron wrote:

  ahah, I asked the same question very recently [1]. Answer by Brendan Eich
> [2].
> I definitely agree that default arguments are a decent alternative. I
> can't recall examples where it wouldn't be enough. Do you have use cases
> where you would use ||= and default argument values couldn't be used?
>
> David
>
> [1] https://twitter.com/DavidBruant/status/210654806732324864
> [2] https://twitter.com/BrendanEich/status/210750515808706561
>
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
>
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