[boost] Re: enable_if review

From: Jaakko Jarvi (jajarvi_at_[hidden])
Date: 2003-10-10 11:49:07

In our last exciting episode David Abrahams wrote:
> > 1. lazy_enable_if
> >
> > Shouldn't be this named apply_enable_if. It very similar to the appropriate
> > MPL concept and seems logical to be named the same.

> I had the same thought, FWIW.  I just couldn't make it sound right in
> the ear, though.  

> On second thought, I wonder if we need it at all.  Isn't 

>    mpl::apply_if<condition, nullary_metafunction, disabled>::type

> equivalent, where disabled is a struct with no nested ::type?

This wouldn't work. At the outermost level (apply_if), ::type always
exists, so this would lead to an error, not disabling the function, on
compilers (e.g. g++) where SFINAE is not applied when the invalid type
occurs nested in another instantiation.

  Jaakko & Jeremiah