Re: [Boost-users] [mpl] nested lambdas?

From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2005-10-05 19:27:50

Geoffrey Romer writes:
> Suppose I'm tying to build a nested lambda expression, like so
> (typename...::type omitted for simplicity):
>
> lambda<higher_order_func<lambda<foo<_1> >, _2> >
>
> - Is this legal?

Yes, although the semantics is probably not what you are trying to
achieve: for the purpose of inline metafunction composition, 'lambda'
is just a metafunction without any special status, and is treated as
such. The 'apply' test
(http://cvs.sourceforge.net/viewcvs.py/boost/boost/libs/mpl/test/apply.cpp?rev=1.5&view=markup)
actually illustrates this and similar cases well.

> - Does the _1 refer to the first argument of the inner lambda, or of
> the outer lambda?

The outer one.

> - Can the above be overridden? I.e. what if I want to refer to the
> arguments of both lambdas within the inner lambda?

It's not currently supported, but it's on the TODO list --
see http://thread.gmane.org/gmane.comp.lib.boost.devel/115924.

-- 
Aleksey Gurtovoy
MetaCommunications Engineering