On Feb 3, 2009, at 3:35 PM, Vladimir Batov wrote:
I'd like to suggest extending (no disruption to the existing interface/users) the existing
template<class Target, class Source> Target lexical_cast(Source const& arg)
interface with
template<class Target, class Source> Target lexical_cast(Source const& arg, Target const& default_value)
The behavior of the latter would be to return the 'default_value' if/ when the conversion fails. That communicates the fact of the conversion failure differently (without an exception thrown) as IMHO a conversion failure is not really that exceptional (rather common).
Last time this topic came up I took some time to modify lexical_cast.hpp (starting from boost 1.37.0 source) to fit this interface. I also added a specialization for boost::optional<T> that instead of throwing bad_lexical_cast, simply returned an empty optional type (which required rewriting optional_io.hpp, as I believe it has a bug: https://svn.boost.org/trac/boost/ticket/2659 ). Here's some example usage: http://codepad.org/hn6MjKjm modified lexical_cast.hpp: http://codepad.org/JAA4Me9Q modified optional_io.hpp: http://codepad.org/8ablH1Nq I too would love to see these extensions to lexical_cast, but in the meantime I've been using these modified versions. Just thought I'd share them in case anyone else was interested. -- Andrew Troschinetz Applied Research Laboratories