Rick Waldron wrote:
On Tue, Jun 12, 2012 at 11:45 AM, Ryan Florence <rpflore...@gmail.com
<mailto:rpflore...@gmail.com>> wrote:
I use ||= very regularly in ruby and coffeescript, both of which
have default arguments.
I don't see Ryan's mail.
First, as we've discussed in the past, ||= in Ruby is not what we've
proposed. In JS, assignment operators expand like so
A op= B; ~~> A = A op B;
with of course a temporary to hold the base of A (which must evaluate to
a Reference) so side effects are not duplicated.
In Ruby IIRC, A ||= B is A = B unless A (hope I have this right).
This matters if A is an accessor. Do we always set A, even to its
current value if truthy?
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);
...
},
...
};
This is handy, and also idiomatic but to multiple languages.
It's worth considering, but we need to wrestle the semantics to the
ground. If the left-hand side's value is truthy, I argue there should be
no useless assignment of that value to the left-hand side.
IOW I favor Ruby semantics. This breaks from JS's C-inspired assignment
operators, but perhaps we can live with it.
/be
_______________________________________________
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss
