
[/ Copyright (C) 2009-2012 Lorenzo Caminiti ]
[/ Distributed under the Boost Software License, Version 1.0 ]
[/ (see accompanying file LICENSE_1_0.txt or a copy at ]
[/ http://www.boost.org/LICENSE_1_0.txt) ]
[/ Home at http://www.boost.org/libs/local_function ]

[section Introduction]

/Local functions/ (a.k.a., [@http://en.wikipedia.org/wiki/Nested_function /nested functions/]) are a form of /information hiding/ and they are useful for dividing procedural tasks into subtasks which are only meaningful locally, avoiding cluttering other parts of the program with functions, variables, etc unrelated to those parts.
Therefore, local functions complement other structuring possibilities such as namespaces and classes.
Local functions are a feature of many programming languages, notably [@http://en.wikipedia.org/wiki/Nested_function#An_example Pascal] and [@http://en.wikipedia.org/wiki/Nesting_(computing)#In_programming Ada], yet lacking from __CXX03__ (see also __N2511__).

Using __CXX11_lambda_functions__, it is possible to implement local functions by naming lambda functions assigning them to local variables.
For example (see also [@../../example/add_cxx11_lambda.cpp =add_cxx11_lambda.cpp=]):

[add_cxx11_lambda]

This library allows to program local functions portably between __CXX03__ and __CXX11__ (and with performances comparable to lambda functions on __CXX11__ compilers).
For example (see also [@../../test/add.cpp =add.cpp=]):

[add]

This library supports the following features for local functions:

* Local functions can capture, or better [@http://en.wikipedia.org/wiki/Name_binding /bind/], any of the variables from the enclosing scope (a function together with its captured variables is also called a [@http://en.wikipedia.org/wiki/Closure_(computer_science) /closure/]).
* The local function body is programmed using the usual C++ statement syntax (as a consequence, compiler errors and debugging retain their usual meaning and format).
* Local functions can be passed as template parameters so they can be conveniently used with STL algorithms and other templates.
[footnote
This is a strength with respect to __CXX03__ functors implemented using local classes which cannot be passed as template parameters (see __N2657__ and the __Alternatives__ section).
]
* However, local functions must be specified within a declarative context (e.g., at a point in the code where local variables can be declared) thus they cannot be specified within expressions.
[footnote
This is a weakness with respect to __CXX11_lambda_functions__ which can instead be specified also within expressions (see the __Alternatives__ section).
]

See the __Alternatives__ section for a comparison between this library, __CXX11_lambda_functions__, __Boost_Phoenix__, and other C++ techniques that implement features related to local functions.

[endsect]

