Re: [boost] Formal Review Request: TypeErasure

Subject: Re: [boost] Formal Review Request: TypeErasure
From: Karsten Ahnert (karsten.ahnert_at_[hidden])
Date: 2012-06-15 16:56:44

On 06/15/2012 09:21 PM, Steven Watanabe wrote:
> AMDG
> 
> On 06/13/2012 01:46 PM, Karsten Ahnert wrote:
>> On 05/22/2012 10:34 PM, Steven Watanabe wrote:
>>> I'd like to request a formal review of the
>>> TypeErasure library that I've posted about
>>> several times before here.
>>
>> I am not sure if this has already been a topic here, but I wonder if the
>> any type can be default constructible? The docs state that this is
>> possible via type_erase::constructible< _self() >, but it is not
>> working, at least for me.
>>
> 
> What do you want the default constructor to do?
> constructible<_self()> captures the default
> constructor of the stored type.  However, it
> doesn't map to a default constructor of any<>
> because there would be no way to know what the
> contained type is.
> 
> typedef mpl::vector<..., constructible<_self()> > Concept;
> T value;
> any<Concept> x(value);
> any<Concept> y(binding_of(x));
> 
> y contains a default constructed instance of T.

Ok, I see. I misunderstood the docs: "Now, suppose that we want a
default constructor?" refers to the default construction of T.

> Now, as far as having a default constructor that
> sets the any to a null state goes, I intended
> to implement it, but forgot about it.  I should
> have it in before the review, though.

Exactly, I missed the default constructor of any, initializing any to a
null state.