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Subject: [boost] numeric_cast
From: Brandon Kohn (blkohn_at_[hidden])
Date: 2011-06-16 09:44:06


Recently I was creating a new numeric type which I wanted to use along
with boost::numeric_cast. I read over the docs and examples and found
that it seemed to support (at least partially) the notion of policy
driven casting operations. I was unable to figure out how one might use
a custom conversion or overflow policy along with the actual
boost::numeric_cast<N>(x) function. In the end I created a workaround
which seemed to work nicely:

template <typename ConversionTraits, typename EnableIf = void>
struct numeric_cast_traits
   typedef def_overflow_handler overflow_handler;
   typedef UseInternalRangeChecker range_checker;
   typedef Trunc
         typename ConversionTraits::source_type
> rounding_policy;

template <typename Target, typename Source>
inline Target numeric_cast( Source arg )
   typedef boost::numeric::conversion_traits<Target, Source> conv_traits;
   typedef numeric_cast_traits< conv_traits > cast_traits;
   typedef boost::numeric::converter
     , Source
     , conv_traits
     , typename cast_traits::overflow_handler
     , typename cast_traits::rounding_policy
     , boost::numeric::raw_converter< conv_traits >
     , typename cast_traits::range_checker
> converter;
   return converter()(arg);

This change allowed me to easily customize the numeric_cast function for
individual conversion types.

Did I miss something in the official library? If not, would this change
be something good to go in?


Brandon Kohn

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