Re: [boost] [SoC][string_cvt] The proposal for string conversions library.

From: Jeff Garland (jeff_at_[hidden])
Date: 2006-05-05 11:52:04

Oleg Abrosimov wrote:
> Alexander Nasonov:
> 
> in the "Lexical Conversion Library Proposal for TR2" (N1973) proposal 
> Kevlin Henney and Beman Dawes states:
> 
> "Since either the source or target are usually strings, why not provide 
> separate to_string(x) and string_to<t>(x) functions?
> 
> The source or target isn't always a string. Furthermore, the from/to 
> idea cannot be expressed in a simple and consistent form. The illusion 
> is that they are easier than lexical_cast because of the name. This is 
> theory. The practice is that the two forms, although similarly and 
> symmetrically named, are not at all similar in use: one requires 
> explicit provision of a template parameter and the other not. This is a 
> simple usability pitfall that is guaranteed to catch experienced and 
> inexperienced users alike -- the only difference being that the 
> experienced user will know what to do with the error message."
> 
> 
> for me it is reasonable enough to require a symmetric usage of 
> from_string/string_from functions I've proposed.

Well, I can buy into the idea that the target is always a 'string'.  And 
frankly I've never used any other sort of target/source for these kinds 
of conversion.  But your're still not responding to the core of my 
question.  The problem is "what's a string"?  Some possibilities:

std::wstring
std::string
std::basic_string<uchar> //some sort of unicode string
std::vector<char>  //and variants thereof
sti::rope
jeffs_really_cool_string_class // ;-)

I think even if the plan is to limit to 'a string' you will need to 
support these sort of options.  Which means you need a second templat 
argument.

Which probably means you need to clearly define the concept of a string 
w.r.t these conversions.  And perhaps that's how it differentiates from 
lexical_cast.  That is lexical_cast
requires Target == InputStreamable, DefaultConstructable and Source == 
OutputStreamable.  What are your concept requirements?

Jeff