[Boost-bugs] [Boost C++ Libraries] #12447: Need some help with a lambda expression exercize

Subject: [Boost-bugs] [Boost C++ Libraries] #12447: Need some help with a lambda expression exercize
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2016-09-10 20:34:32

#12447: Need some help with a lambda expression exercize
------------------------------------+-----------------------
 Reporter:  JUAN DENT <juandent@…>  |      Owner:  agurtovoy
     Type:  Support Requests        |     Status:  new
Milestone:  To Be Determined        |  Component:  mpl
  Version:  Boost 1.61.0            |   Severity:  Problem
 Keywords:                          |
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 Hi,
 I am studying "C++ Template Metaprogramming" and stuck in
 exercise 3-6 which states:

 "Build a lambda expression that has functionality equivalent to 'twice'.
 Hint: mpl::apply is a metafunction!"

 Now twice is defined like so:
 {{{
 #!C++
 template<class F, class X>
 struct twice
 : mpl::apply< F, typename mpl::apply<F,X>::type>
 {};
 }}}

 The book defines a lambda expression as: "callable metadata. they have 2
 basic forms: metafunction classes and placeholder expressions".

 Thank you for your help!
 Juan

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/12447>
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