I agree that execAll() is not a 100% winner, more like a clean-up of a quirky
corner. But exec() in “multi” mode has a surprising amount of pitfalls:
* /g flag must be set
* lastIndex must be 0
* can’t inline the regex, because it is needed as a pseudo-iterator (more of an
anti-pattern, anyway, but still)
* side effects via lastIndex may be a problem
All of these would go away with a execAll(). The thing I’m not sure about is
how frequently exec() is used that way. String.prototype.match() does indeed
cover a lot of use cases. So does String.prototype.replace().
On Aug 29, 2013, at 9:45 , Brendan Eich <bren...@mozilla.com> wrote:
> Axel Rauschmayer wrote:
>>> The fact that s.match(/re/g) returns the array of all matches (with
>>> captures) sucks some of the oxygen away from any /re/g.execAll(s) proposal.
>>>
>>> But String.prototype.match has perlish hair (e.g., those capture groups
>>> showing up in the result array).
>>
>> Really? AFAICT, only the complete matches (group 0) are returned.
>>
>
> Sorry, of course you are right -- how soon I forget -- the subgroups show up
> only in each exec result array, but are dropped from the match result.
>
> So hair on the other side of the coin, if you will. A naive iterator that
> calls exec would return, e.g.,["ab", "b"] for the first iteration given r and
> s as follows:
>
> js> r = /.(.)/g
> /.(.)/g
> js> s = 'abcdefgh'
> "abcdefgh"
> js> a = s.match(r)
> ["ab", "cd", "ef", "gh"]
> js> b = r.exec(s)
> ["ab", "b"]
>
> Is this what the programmer wants? If not, String.prototype.match stands
> ready, and again takes away motivation for an eager execAll.
>
> But programmers wanting exec with submatches could use a lazy form:
>
> js> r.lastIndex = 0
> 0
> js> RegExp.prototype.execAll = function (s) { let m; while (m = this.exec(s))
> yield m; }
> (function (s) { let m; while (m = this.exec(s)) yield m; })
> js> c = [m for (m of r.execAll(s))]
> [["ab", "b"], ["cd", "d"], ["ef", "f"], ["gh", "h"]]
>
> /be
>
--
Dr. Axel Rauschmayer
a...@rauschma.de
home: rauschma.de
twitter: twitter.com/rauschma
blog: 2ality.com
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