Re: [boost] [type_erasure] [docs]contrast with boost::any

Subject: Re: [boost] [type_erasure] [docs]contrast with boost::any
From: Larry Evans (cppljevans_at_[hidden])
Date: 2012-07-23 19:34:54

On 07/23/12 15:37, Larry Evans wrote:
> On 07/18/12 00:13, Lorenzo Caminiti wrote:
>> Hello all,
>>
>> *** The review of Steven Watanabe's proposed Boost.TypeErasure library
>> begins on July 18, 2012 and ends on July 27, 2012. ***
>>
> The page:
> 
> http://steven_watanabe.users.sourceforge.net/type_erasure/libs/type_erasure/doc/html/boost_typeerasure/basic.html
> 
> says:
> 
> x is approximately equivalent to a boost::any
> 
> however, it doesn't say how te::any differs from boost::any.
> 
> The attached shows that a boost::any can change it's
> type, and, as such, is somewhat like boost::variant.
> However, te::any, once it's created, cannot change
> it's type, AFAICT.  At least that's what the
> attached code indicates when compiled with:
> 
>  #define SHOW_TE_FIXED_TYPE
> 
A simplified version of that code (which doesn't require
demangled_type_name), is attached.

The attached also suggests that, when multiple placeholders
are in the concept, the unary any *requires* a binding
argument.  This is shown by trying to compile the attachment
with:

          #define SHOW_BINDINGS_MUST_BE_COMPLETE

In contrast, the example here:

http://steven_watanabe.users.sourceforge.net/type_erasure/libs/type_erasure/doc/html/boost_typeerasure/basic.html

shows no binding is needed because the only placeholder
in the concept is the default, _self.

HTH.

-regards,
Larry