[boost] return type of function objects

From: vamshi mugu (boost_vam_at_[hidden])
Date: 2002-10-31 20:04:16

This is the GeneratorConcept from 
http://www.boost.org/boost/concept_check.hpp

template <class Func, class Return>
  struct GeneratorConcept
  {
    void constraints() {
      const Return& r = f();   // require operator() 
      ignore_unused_variable_warning(r);
    }
    Func f;
  };

---- and this is the UnaryFunctionConcept 

template <class Func, class Return, class Arg>
  struct UnaryFunctionConcept
  {
    // required in case any of our template args are 
const-qualified:
    UnaryFunctionConcept();

    void constraints() {
      r = f(arg); // require operator()
    }
    Func f;
    Arg arg;
    Return r;
  };

----------------------------
As it is, the UnaryFunctionConcept requires that
'Return' be non-const (while there is no such
requirement on the 'Return' in GeneratorConcept) 

Is there a good reason why these two are different ?
That is, would 
const Return& r = f();   
not work for UnaryFunctionConcept too?

=====
Vamshi Mugu
North Dakota State University

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