Re: [Boost-users] find the largest/most precise of two types

Subject: Re: [Boost-users] find the largest/most precise of two types
From: John Maddock (john_at_[hidden])
Date: 2009-05-20 12:40:02

> I have a bunch of functions that accept two numeric arguments. In the
> case that the types of these arguments are different I want to figure
> out what the return type should be. The rule I would like to use is
> that the largest of the two types should be used for internal
> computations and the return type.
>
> f(someFloat, someDouble) -> double
> f(someFloat, someFloat) -> float
> f(someInt, someFloat) -> float
>
> Is there a way I can do this, perhaps with boost's type_traits?

Take a look at

boost::math::tools::promote_args<....>::type

defined in boost/math/tools/promotion.hpp: it's an implementation detail so 
you probably shouldn't rely upon it, but it should give you a good head 
start.  Note that it treats all integer arguments "as if" they were really 
doubles - so not quite what you asked for - this was done for compatibility 
with the rules in C99 and the upcoming C++ standard that integer arguments 
to math functions should be treated as doubles.  Should be easy to adapt to 
what you want though,

HTH, John.