On Wed, Sep 28, 2011 at 11:05 PM, Dean Landolt <[email protected]> wrote:
> > > On Wed, Sep 28, 2011 at 10:06 PM, Mike Shaver <[email protected]>wrote: > >> On Wed, Sep 28, 2011 at 9:11 PM, Brendan Eich <[email protected]> >> wrote: >> > No worries, array extras are a great addition, we just need to keep >> rolling. >> >> Oh, no offense taken. I just meant to say that there may be >> consistency-with-existing-pattern reasons to prefer one hole behaviour >> over another, is all. >> > > > Another reason to prefer the current hole-hopping behavior for array extras > is that it's currently the *only* way to get any efficiency advantage > sparse arrays. So regardless of rationale, it's strictly more featureful and > almost certainly the intended behavior if, as a developer, you're aware of > holes. > > But to reiterate the point I made earlier, in order for libraries to take > complete ownership of looping constructs we need a better way to detect > holes in userland -- something that can be optimized. I was trying to think > of a way to overload Array.prototype.indexOf and lastIndexOf but since we > don't have a type for holes this isn't really feasible (I'd thought of using > NaN as a sigil here as it's otherwise untestable in indexOf, but this would > be wrong on so many levels). > Holes can be detected and skipped by using the "in" operator... var array = [ 1, , 3, , 5 ]; for ( var i = 0; i < array.length; i++ ) { // Skip accessing in sparse arrays if ( i in array ) { console.log( array[i] ); } } > Regardless of where it goes (on Array, Array.prototype, or in a system > module), all we really need is something like a function that takes an index > and direction and returns the next hole's start index and length (or end > index). I'll put together a proposal if this isn't too controversial. > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
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