Re: [boost] [review] string convert

Subject: Re: [boost] [review] string convert
From: Vladimir Batov (vbatov_at_[hidden])
Date: 2011-05-11 18:19:44

> Vicente BOTET <vicente.botet <at> wanadoo.fr> writes:
>
> ... and second partial template specialization of a convert_to functor (with
> two type template parameters Target and Source) ...
> 
> The library contains a lot of examples of partial specializations as for
> example the optional
> conversions. I have added a dummy complete specialization for std::string,
> bool and everything is OK.

The problem: there may be two independent specialization streams -- by the
Source type and by the Target type. For example,

convert_to<T, char const*>
convert_to<T, wchar_t const*>
convert_to<T, string const&>
convert_to<T, wstring const&>
convert_to<T, char []>

string-to-type share the same implementation of a partial specialization for the
Source type -- a string-like type. Then, one wants to specialize/optimize by the
Target type. Say, specifically for bool and tries to provide

convert_to<bool, int>
convert_to<bool, long int>
convert_to<bool, short int>
convert_to<bool, string-like-type>

The latter bool-to-string-like-type is a partial specialization again as it
takes any string-like type (char const*, std::string, etc.).

Now type-to-string and bool-to-string partial specializations seem to
match/clash for

bool v = convert_to<bool>("false");

I vaguely remember having that issue 2-3 years back. That's why I had to split
Target and Source types by convert<T>::from(S). 

I did look at your examples/tests in the conversion/libs/test directory. They
all seem to be complete specializations for a particular Target type. The
std/string.hpp does not cover the above-mentioned use-case as it deals with
type-to-std::string (again specialization by Target type) conversion. That is, I
did not find any specializations by the Source type like any-string-to-type
conversion tests/examples. That might be the reason you have not had the problem
that I described. :-)

V.