[Boost-users] Re: [MPL] map question

From: David Abrahams (dave_at_[hidden])
Date: 2004-12-22 13:58:50

Aleksey Gurtovoy wrote:

> 
>>From http://www.boost.org/libs/mpl/doc/refmanual/protect.html:
> 
>     'protect' is an identity wrapper for a Metafunction Class that 
>     prevents its argument from being recognized as a bind expression.
> 
> Actually, the above definition is incomplete; should be:
> 
>     'protect' is an identity wrapper for a Metafunction Class that 
>     prevents its argument from being recognized as a bind/placeholder 
>     expression.
> 
> The main usage for 'protect' is to prevent parametrized metafunction classes
> from being accidentally treated as a placeholder expression simply because
> their arguments happened to embed a placeholder. 

Hum.  Seems a bit counterintuitive that protect doesn't apply equally
well to this case.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com