[boost] Re: lexical_cast "Future directions"

From: Early Ehlinger (earlye_at_[hidden])
Date: 2002-12-28 20:22:41

"Terje Slettebø" <tslettebo_at_[hidden]> wrote:
> e.g. the following one gives the same problem, not solved with only
> checking for if source type equals target type:
>
> std::string str=boost::lexical_cast<std::string>(' '); // Space character,
> throws exception

Indeed.  I took a look at the proposed fix and it seems to fix both
problems.  Thank you for taking the time to implement the new solution.

As a devil's advocate, consider, e.g., Borland's AnsiString class (part of
their VCL and CLX libraries, basically a class that represents the intrinsic
String type in Pascal/Delphi):

AnsiString foo = "Hello there";
std::string str = boost::lexical_cast< std::string >( foo );  // exception
for same reason!

This leads me to wonder if there isn't a more generic solution to the
problem.  For example, it might be useful to have a mechanism to determine
if source is a string type and if so, use an implementation that looks
something like this:

std::stringstream temp;
temp << source;
return TargetType( temp.str().c_str() );

When I say "string type", I mean any type that represents the concept of a
string, not just those that are implemented via std::basic_string.  Not sure
what exactly the best way to do this is; perhaps a lexical_cast_traits<>
template that the user must provide to help out?  So right after I include
the definition of AnsiString, I could do something like this:

template<> struct lexical_cast_traits< AnsiString > : public
lexical_cast_string_type { };

And now lexical_cast would "know" that AnsiString is a string type.

Similar things could be done to support CString from MFC as well as the
zillions of other string implementations out there.

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