Re: [boost] [type_erasure] Difficulties with const

Subject: Re: [boost] [type_erasure] Difficulties with const
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2012-09-13 17:10:22

AMDG

On 09/13/2012 01:42 PM, Christophe Henry wrote:
> 
> * ping *
> 

I'm sorry.  I don't think I received the original message.

> 
>> <snip>
>> namespace boost {
>> namespace type_erasure {
>> template<class C, class T, class Base>
>> struct concept_interface< ::getName<C, T>, Base, C> : Base
>> {
>>    T getName()
>>    { return call(::getName<C, T>(), *this); }
>> };
>> }
>> }
>>
>> <snip>
>>
>> This compiles and outputs as expected.
>>
>> Problem 1: This will not compile
>> std::cout << "data: " << (*it).getName() << std::endl;
>>

concept_interface<...>::getName needs to
be declared const for this to work.

>> Hmmm ok not so bad. I'll gladly pay the extra line. (interestingly, it
>> would compile and work without const)
>>
>>
>> Problem 2: if I use the MEMBER macro:
>>
>> BOOST_TYPE_ERASURE_MEMBER((has_getName), getName, 0);
>> typedef any<
>>          mpl::vector<
>>              has_getName<std::string const&()>,
>>              relaxed_match,
>>              copy_constructible<>,
>>              typeid_<>
>>          >,
>>           const _self&
>>      >
>> AnyNameable;
>>
>> Then the code does not compile, unless I accept to give up all of my
>> consts.

For a constant member function use:

has_getName<std::string const&(), const _self>

>> On one hand, I will find it a easier job to sell type_erasure with the
>> macro, OTOH, I will not give up my consts ;-)
>>
>> Would it be possible to have the macro AND const-correctness?
>>

In Christ,
Steven Watanabe