Thorsten Ottosen wrote:
Hi Matthias,
"Matthias Kaeppler" <nospam@digitalraid.com> wrote in message news:d0ff4g$7rm$1@sea.gmane.org... | Hello, | | because of the lack of a generic adaptor which indirects operations on | pointers to the pointees, i.e. sorting a collection of pointers with | predicates applying to the pointees, I have come up with two classes, | indirecter_unary and indirecter_binary which do exactly that (thanks | again to the people from boost users and comp.lang.c++ for assisting | me). Both adaptors accept adaptable function objects as well as plain | functions.
these classes are useful when we need to use a class; boost.bind won't work since we don't know what type it returns.
I have been playing with similar functionality for Boost.Pointer Container because the ptr_set class needs it.
I have a question, though. I'm thinking, what is the benefit of your approach compared to
template< class Fun > class indirect_fun { Fun fun; public: typedef typename result_of<Fun>::type result;
indirect_fun( Fun f ) : fun(f) { }
template< class T > result operator( T* r ) const { return fun( *r ); }
template< class T, class U > result operator( T* r, U* r2 ) const { return fun( *r, *r2 ); }
// etc };
br
-Thorsten
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There are several problems with this template. First, it's not an "Adaptable Binary Function" or "Adaptable Unary Function", because it fails to provide the required typedefs result_type and argument_type, and result_type and first_argument_type, second_argument_type respectively. Second, it might fail to compile when Fun takes arguments by reference. I had problems at this part, that's why I used the boost type traits library to remove any references on the type first, and only work on "raw" const-pointers. Third, (correct me if I'm wrong, I haven't used it before), as far as I understand, the result_of class template won't work if you instantiate your template with a plain function. Instead, boost::unary_traits and boost::binary_traits take care of the right typedefs if you want your adaptor to work with both functors and functions. -- Matthias Kaeppler