Re: [boost] [algorithm] to_lower_copy / to_upper_copy with no output param assumes sequence to be same as input

Subject: Re: [boost] [algorithm] to_lower_copy / to_upper_copy with no output param assumes sequence to be same as input
From: Sebastian Karlsson (sairony_at_[hidden])
Date: 2011-06-23 07:26:21

2011/6/23 Olaf van der Spek <ml_at_[hidden]>:
> On Wed, Jun 22, 2011 at 3:05 PM, Sebastian Karlsson <sairony_at_[hidden]> wrote:
>> It would seem: std::string foo = boost::algorithm::to_lower_copy<
>> std::string >( "bar" ); isn't valid. Instead one has to do for
>> example: std::string foo = boost::algorithm::to_lower_copy(
>> std::string( "bar" ) ), which while perhaps just as terse and natural
>> creates an extra unneeded temporary. I propose the following addition,
>> as well as one for to_upper_copy:
>>
>>                template<typename OutputSequenceT, typename RangeT>
>>                inline OutputSequenceT
>>                        to_lower_copy(
>>                        const RangeT& Input,
>>                        const std::locale& Loc=std::locale())
>>                {
>>                        OutputSequenceT Output( ::boost::begin( Input ), ::boost::end( Input ) );
>
> Doesn't this also do an unnecessary copy?
>
> Olaf

It does, but it uses one less which as stated is a prime candidate for
NRVO. The current approach needs one temporary for the return value as
well as a temporary for argument conversion, which is basically only
there to inform about the return type.

Kind regards,
Sebastian Karlsson