ceph/src/boost/libs/bind/doc/bind/limitations.qbk

   1 [/
   2  /  Copyright (c) 2001, 2002 Peter Dimov and Multi Media Ltd.
   3  /  Copyright (c) 2003-2008 Peter Dimov
   4  /
   5  / Distributed under the Boost Software License, Version 1.0. (See
   6  / accompanying file LICENSE_1_0.txt or copy at
   7  / http://www.boost.org/LICENSE_1_0.txt)
   8  /]
   9
  10 [section:limitations Limitations]
  11
  12 As a general rule, the function objects generated by `bind` take their
  13 arguments by reference and cannot, therefore, accept non-const temporaries or
  14 literal constants. This is an inherent limitation of the C++ language in its
  15 current (2003) incarnation, known as the [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm forwarding problem].
  16 (It will be fixed in the next standard, usually called C++0x.)
  17
  18 The library uses signatures of the form
  19
  20     template<class T> void f(T & t);
  21
  22 to accept arguments of arbitrary types and pass them on unmodified. As noted,
  23 this does not work with non-const r-values.
  24
  25 On compilers that support partial ordering of function templates, a possible
  26 solution is to add an overload:
  27
  28     template<class T> void f(T & t);
  29     template<class T> void f(T const & t);
  30
  31 Unfortunately, this requires providing 512 overloads for nine arguments, which
  32 is impractical. The library chooses a small subset: for up to two arguments,
  33 it provides the const overloads in full, for arities of three and more it
  34 provides a single additional overload with all of the arguments taken by const
  35 reference. This covers a reasonable portion of the use cases.
  36
  37 [endsect]