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Subject: Re: [boost] [string] proposal
From: Ivan Le Lann (ivan.lelann_at_[hidden])
Date: 2011-01-29 12:00:18

----- "Dean Michael Berris" <mikhailberis_at_[hidden]> wrote :

> On Sat, Jan 29, 2011 at 8:07 PM, Ivan Le Lann <ivan.lelann_at_[hidden]>
> wrote:
> >
> > Dean Michael Berris wrote :
> >
> >>
> >> But c_str() doesn't have to be part of the string's interface.
> >
> > *My* *guess* is that Artyom think that:
> >
> >  os_func ((s1 + s2 + s3 + ... + s100).c_str()); // s for std::string
> >
> > is dramatically faster than:
> >
> >  os_func ((c1 + c2 + c3 + ... + c100).to_string().c_str()); // c for
> "boost::chain"
> >
> And this is precisely my point as well: the one that uses boost::chain
> is perfectly suited for this kind of use case in both efficiency and
> clear-cut semantics. I for one don't like to make to_string() a member
> either -- I much rather make it a conversion operator so boost::chain
> (if we're going to call it that) can be used where interfaces take a
> std::string.

[Note: I'm all for chains/ropes/etc, only looking for corner cases]

I definitely agree for my example, which is a pure rope demo.
linearize(chain) can give a c_str at no cost for trivial chains, and
is not heavier than std::string::operator+ for non-trivial chains.

Now looking at Artyom example makes me consider the quite common
case where the desired output is not c_str but std::string itself.
Add move optimizations on top of that:

func_taking_std_string ( /*linearize*/ (my_chain_func ()));
func_taking_std_string ( (my_string_func ()));

No matter the way you put it, you have one unnecessary allocation,
because std::string has no move constructor from chain (yet).
For people eventually throwing their boost::chain into std::string,
we're basically killing all move/RVO optimizations.

Am I missing something?


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