Re: [boost] RFC: type erasure

Subject: Re: [boost] RFC: type erasure
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2011-05-23 18:01:38

AMDG

On 05/23/2011 02:34 PM, Vicente Botet wrote:
> 
> I like how concepts are materialized using a template class that implements
> the default behavior of the concept and that can be specialized to map type
> to concepts. I understand that you need a second step to introduce the
> functions themselves specializing concept_interface.
> 
> What I don't understand is the overloading issues. Could you use a concrete
> example to try to clarify the problems you have addressed?
> 

Okay.  Problem 1: Name hiding for member functions.

typedef mpl::vector<
    callable<int(int)>,
    callable<double(double)>
> test_concept;

If we just use the basic definition of
concept_interface, the second overload
will hide the first since the inheritance
structure looks like:

struct callable1 {
    int operator()(int);
};

struct callable2 : callable1 {
    double operator()(double);
};

For free functions, I had a problem akin to name
hiding when I defined a single namespace scope
overload with concept_interface arguments.  Using
an inline friend function that takes the derived
type works with some care to avoid duplicate
definitions.

You can check the tests for details on what I expect
to work.  Most of the tests for specific concepts
have a test_overload test case.

In Christ,
Steven Watanabe