Jason Orendorff wrote:
On Thu, Jul 5, 2012 at 12:54 PM, Brendan Eich<[email protected]> wrote:
Allen privately observed that Array forEach skips holes, matching for-in.
That counts for a lot with me -- we have only a blind
for(i=0;i<a.length;i++)... loop not skipping holes, but of course it
wouldn't. That is weak precedent on which to build for-of.
In what sense is that precedent weak? It seems a stronger precedent
than forEach on every axis; arguably it's one of the most-trodden
cowpaths in programming, in any language.
That's too general a claim to be self-certifying. I <3 C but in JS, lots
of a.forEach(function (e) {...}) usage these days. Kids are into FP.
for-in is a kind of anti-precedent, for array iteration.
The point is for-in *in addition to* forEach and other Array extras skip
holes. Not for-in by itself as motivation, really, just consistency of
all but for-of as implemented.
Map may win at some point, who knows? It's not winning if one wants
an array, numeric indexing, .length, the usual prototype methods.
I agree Map is somewhat beside the point. TC39 should spec what's best
for developers net of everything. Even if that's matching for-in. But
the purpose of for-of is to address the shortcomings of for-in;
following it just for the sake of consistency would be self-defeating.
I think your focus is pulled by for-in too much. It happens to match the
Array extras and this makes a happy consistency, but the main precedent
is forEach, along with the rest of the extras which agree on skipping holes.
If there's a botch here, it is holes in arrays, or rather: arrays not
being like Python lists, instead being barely-specialized
objects-with-properties. But that's a done deal. From that, holes follow.
From holes, skipping or not skipping consistently must follow. So far
we've been consistent over the many years: for-in, forEach, etc. all skip.
The C-style loop is blind to property existence so is really a different
animal. It's true people are told not to use for-in on arrays, but that
does not make them use for(;;). Instead they seem to reach for forEach.
Which skips holes.
Reasoning about latent bugs due to skipping holes is perilous and wants
empirical studies, some evidence, a few burning anecdotes. Got any?
/be
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