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[ceph.git] / ceph / src / boost / libs / tti / doc / tti_why.qbk

[/ 
  (C) Copyright Edward Diener 2011
  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE_1_0.txt or copy at
  http://www.boost.org/LICENSE_1_0.txt).
]

[section:tti_reason Why the TTI Library ?]

In the Boost Type Traits library there is compile time functionality for 
querying information about a C++ type. This information is very useful 
during template metaprogramming and forms the basis, along with the 
constructs of the Boost MPL library, and some other compile time 
libraries, for much of the template metaprogramming in Boost.

One area which is mostly missing in the Type Traits library is the ability 
to determine what C++ inner elements are part of a type, where the inner 
element may be a nested type, function or data member, static function or 
static data member, or class template.

There has been some of this functionality in Boost, both in already existing
libraries and in libraries on which others have worked but which were 
never submitted for acceptance into Boost. An example with an existing Boost
library is Boost MPL, where there is functionality, in the form of macros and metafunctions, 
to determine whether an enclosing type has a particular nested type or nested 
class template. An example with a library which was never submitted to Boost 
is the Concept Traits Library from which much of the functionality of this 
library, related to type traits, was taken and expanded.

It may also be possible that some other Boost libraries, highly dependent 
on advanced template metaprogramming techniques, also have internal 
functionality to introspect a type's elements at compile time. But to the best 
of my knowledge this sort of functionality has never been incorporated in 
a single Boost library. This library is an attempt to do so, and to bring  
a recognizable set of interfaces to compile-time type introspection to Boost 
so that other metaprogramming libraries can use them for their own needs.

[endsect]