[PATCH] Add FilteredArgList to represent filtered arglist

[David Blaikie]

On Tue, May 28, 2013 at 10:48 AM, Rui Ueyama <ruiu at google.com> wrote:

> On Mon, May 27, 2013 at 7:35 AM, David Blaikie <dblaikie at gmail.com> wrote:
>
>>
>> On May 26, 2013 12:37 PM, "Rui Ueyama" <ruiu at google.com> wrote:
>> >
>> >
>> >> > +/// FilteredArgList - ArgList with filters. Useful to be used in
>> >> > +/// range-based for loop to iterate over filtered arguments.
>> >>
>> >> Could we just have/use a generic range abstraction (essentially a
>> simple class template with two iterator members, one returned by begin, the
>> other by end) rather than writing a custom type here?
>> >
>> > What if begin is called twice? Is it okay to return the same object,
>> not a new one?
>>
>> If this is any kind of common iterator it must have the usual/obvious
>> copy semantics (that's an iterator requirement) - essentially copying the
>> result of begin should be as good as calling begin twice or there's
>> something very strange/surprising going on (which isn't unheard of in
>> llvm's iterators - so feel free to correct/tell me these are weird
>> iterators that require a special case - I've not looked at them enough to
>> know either way yet)
>>
> No there's no such weird iterator in LLVM as far as I know. I just thought
> that we might want to avoid the overhead of copying the result of begin,
> which can be avoided by this patch. Or am I worry too much?
>

Yeah, certainly worrying too much - iterators generally need to be cheap to
copy & many algorithms will/should treat them as such. These ones certainly
are, so far as I can tell - they're just SmallVector iterators, which are
essentially just plain pointers (or the moral equivalent).
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