Re: [boost] [mpl] has_function

Subject: Re: [boost] [mpl] has_function
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-03-27 23:56:43

AMDG

Lorenzo Caminiti wrote:
> It turned out that I only needed to check if a struct is declared
> within one of the base classes or not. This seems simpler that my
> original goal for has_function and I was able to adapt Ingo's code to
> get the job done -- see below. However, I am getting the following
> compiler error:
>
> $ g++ -Wall -Werror test/noinherit/05.cpp
> test/noinherit/05.cpp: In instantiation of ‘const bool
> z::has_contract_f_<x>::value’:
> test/noinherit/05.cpp:34:   instantiated from here
> test/noinherit/05.cpp:31: error: the default argument for parameter 1
> of ‘static char z::has_contract_f_<T>::check(C*, typename
> C::contract_f_<0>*) [with C = x, T = x]’ has not yet been parsed
>
> Do you know how I can get around this error?
> <snip>
>     template<typename T>
>     struct has_contract_f_ {
>     private:
>         typedef char true_t;
>         struct false_t { true_t dummy[2]; };
>         static T* make();
>
>         static false_t check(...);
>         template<typename C> static true_t check(C*,
>                 typename C::template contract_f_<0>* = 0);
>     public:
>         static const bool value =
>                 sizeof(check(make())) == sizeof(true_t); // line 31
>     };
>
> <snip>
>   

Does it work if you pass 0 explicitly instead of using a default argument.

In Christ,
Steven Watanabe