Re: [boost] Re: passing temporaries to mutating algorithms

From: Daniel Wallin (dalwan01_at_[hidden])
Date: 2004-04-13 05:46:30

Thorsten Ottosen wrote:
> "David Abrahams" <dave_at_[hidden]> wrote in message
>>It works generically on lvalues and rvalues, so that if someone hands
>>you a function object f, and some_algo is more efficient when it can
>>modify its first argument in-place, you can do
>>
>>    some_algo( mutate_rvalue(f(),0), x );
> 
> 
> yeah, definitely an improvement, although I wish there was some way of
> putting a static assertion in there. The new error message is a lot worse.

How about this:

   template<class T> struct cant_mutate_const_values
   {
       typedef int type;
   };

   template<class T> struct cant_mutate_const_values<T const>
   {
       typedef typename cant_mutate_const_values::error type;
   };

   template<class T>
   T& mutate_rvalue(T const& x)
   {
       return const_cast<T&>(x);
   }

   template<class T>
   T& mutate_rvalue(T& x, typename cant_mutate_const_values<T>::type = 0)
   {
       return x;
   }

-- 
Daniel Wallin