Re: [Boost-users] [mpl]... is there an mpl::string

Subject: Re: [Boost-users] [mpl]... is there an mpl::string
From: Eric Niebler (eric_at_[hidden])
Date: 2009-04-08 13:08:49

Noah Roberts wrote:
> After reviewing the code it seems that all my concerns are taken care 
> of.  It looks like it indeed iterates each individual character, not the 
> multicharacter literals.  It also looks like iterating <'hel', 'lo w', 
> 'orld', '!'> would be the same as iterating 'hell','o wo','rld!'>.  So 
> pretty damn cool and some interesting techniques.
> 
> That said, I would still contemplate pulling the c_str out of the string 
> container proper.  I would say that the mpl::string is not similar to 
> the std::string in that it actually has to be transformed (requiring 
> complete reconstruction) into a c_str; there's nothing about the 
> mpl::string that renders c_str easier or particular to this container 
> besides our prebias that it should be.  That alone would indicate 
> separation to me but additionally if the c_str was a metafunction 
> separate from the string container, it could be used on any 
> ForwardSequence.
> 
> Something to consider anyway.  Thanks for adding this.

That's not a bad suggestions, and I was on the fence myself about making 
c_str a class static of mpl::string. My reason for doing so was that 
getting a C-style string at compile time is really the only reason to 
use mpl::string, and so accessing it shouldn't incur an extra template 
instantiation.

A separate c_str metafunction might be useful, but to be a proper 
metafunction, it would need to return a type, not a character array. But 
as with Integral Constants, we could make:

   mpl::c_str<FwdSeq>::type::value

synonymous with:

   mpl::c_str<FwdSeq>::value

And mpl::c_str<FwdSeq>::type is probably just a typedef for 
mpl::c_str<FwdSeq>.

Anyway, I've invested enough time in this already and am happy with the 
result. If you'd like to see mpl::c_str<>, would you care to submit a 
patch? Or at least open a feature-request Trac ticket?

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com