[boost] [bind] [patch] support for result_of

Subject: [boost] [bind] [patch] support for result_of
From: Stefan Strasser (strasser_at_[hidden])
Date: 2010-08-15 09:23:30

Hi,

would a full implementation of this patch:

https://svn.boost.org/trac/boost/raw-attachment/ticket/4542/bind.patch

be accepted to Boost.Bind?

it provides support for bind()ing generic function objects and for  
boost::result_of<F(...)> where F is a result of bind().

for example:

struct F{
   template<typename T>
   T operator()(T const &t, int) const{ return t; }

   template<typename Args>
   struct result;
};

the result type depends on the argument type, so instead of  
"result_type", "result" is defined according to boost::result_of:

template<typename T>
struct F::result<F(T const &,int)>{ typedef T type; }

this function object can not be used with bind(), because bind()  
requires F::result_type to be defined.

with the patch, you can bind() the function object, and determine the  
result of the bound function object using result_of:

int main(){
   g(bind(F(),_1,5));
}

template<typename F>
void g(F const &f){
   double doubleres=f(1.234); //F(1.234,5) -> double
   boost::result_of<F(int const &)>::type intres=f(1); // F(1,5) -> int
}

C++ TR1 includes result_of and bind(). it doesn't seem to say anything  
about result_of<bind()-result> though.