On 4/11/2012 1:13 AM, Olaf van der Spek wrote:
On Wed, Apr 11, 2012 at 8:54 AM, Eric Niebler <eric@boostpro.com> wrote:
Calling m.str() creates a temporary std::wstring object, which incurs a dynamic allocation and is slow. Speaking for my own library (xpressive), sub_match has an optimized stream insertion operator. It should be used.
You have to construct a string somewhere, don't you? If you have one already, you could use iterator_range<const char*> instead to avoid a copy.
Yes, I see that lexical_cast has optimizations for iterator_range<wchar_t const *> and a few other, sufficiently 'string-like' types. But sub_match essentially *is* a string-like iterator_range. (It's a std::pair of iterators.) I'm genuinely surprised there's no way to tell lexical_cast that. Instead I have to just know (a) which are the magical types lexical_cast is optimized for and (b) for which it can determine the correct underlying stream character type (hint: the docs are unclear or out of date), and massage my type into one of those before calling lexical_cast. Why?
But my primary objection is below...
You're right, it'd be nice if that just worked.
-- Eric Niebler BoostPro Computing http://www.boostpro.com