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C++ BOOST
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The Boost Lambda Library</title><meta name="generator" content="DocBook XSL Stylesheets V1.48"><link rel="home" href="index.html" title="
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C++ BOOST
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The Boost Lambda Library"><link rel="next" href="ar01s02.html" title="2. Getting Started"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">
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C++ BOOST
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The Boost Lambda Library</th></tr><tr><td width="20%" align="left"> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ar01s02.html">Next</a></td></tr></table><hr></div><div class="article"><div class="titlepage"><div><h1 class="title"><a name="id2753758"></a>
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<span class="inlinemediaobject"><img src="../../../c%2B%2Bboost.gif" alt="C++ BOOST"></span>
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The Boost Lambda Library</h1></div><div><p class="copyright">Copyright © 1999-2002 Jaakko Järvi, Gary Powell</p></div><div><div class="legalnotice"><p>
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The Boost Lambda Library is free software; Permission to copy,
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use, modify and distribute this software and its documentation is granted, provided this copyright
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notice appears in all copies.
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</p></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt>1. <a href="index.html#introduction">In a nutshell</a></dt><dt>2. <a href="ar01s02.html">Getting Started</a></dt><dd><dl><dt>2.1. <a href="ar01s02.html#id2761975">Installing the library</a></dt><dt>2.2. <a href="ar01s02.html#id2762422">Conventions used in this document</a></dt></dl></dd><dt>3. <a href="ar01s03.html">Introduction</a></dt><dd><dl><dt>3.1. <a href="ar01s03.html#id2762467">Motivation</a></dt><dt>3.2. <a href="ar01s03.html#id2762797">Introduction to lambda expressions</a></dt></dl></dd><dt>4. <a href="ar01s04.html">Using the library</a></dt><dd><dl><dt>4.1. <a href="ar01s04.html#sect:introductory_examples">Introductory Examples</a></dt><dt>4.2. <a href="ar01s04.html#sect:parameter_and_return_types">Parameter and return types of lambda functors</a></dt><dt>4.3. <a href="ar01s04.html#sect:actual_arguments_to_lambda_functors">About actual arguments to lambda functors</a></dt><dt>4.4. <a href="ar01s04.html#sect:storing_bound_arguments">Storing bound arguments in lambda functions</a></dt></dl></dd><dt>5. <a href="ar01s05.html">Lambda expressions in details</a></dt><dd><dl><dt>5.1. <a href="ar01s05.html#sect:placeholders">Placeholders</a></dt><dt>5.2. <a href="ar01s05.html#sect:operator_expressions">Operator expressions</a></dt><dt>5.3. <a href="ar01s05.html#sect:bind_expressions">Bind expressions</a></dt><dt>5.4. <a href="ar01s05.html#sect:overriding_deduced_return_type">Overriding the deduced return type</a></dt><dt>5.5. <a href="ar01s05.html#sect:delaying_constants_and_variables">Delaying constants and variables</a></dt><dt>5.6. <a href="ar01s05.html#sect:lambda_expressions_for_control_structures">Lambda expressions for control structures</a></dt><dt>5.7. <a href="ar01s05.html#sect:exceptions">Exceptions</a></dt><dt>5.8. <a href="ar01s05.html#sect:construction_and_destruction">Construction and destruction</a></dt><dt>5.9. <a href="ar01s05.html#id2824949">Special lambda expressions</a></dt><dt>5.10. <a href="ar01s05.html#id2825516">Casts, sizeof and typeid</a></dt><dt>5.11. <a href="ar01s05.html#sect:nested_stl_algorithms">Nesting STL algorithm invocations</a></dt></dl></dd><dt>6. <a href="ar01s06.html">Extending return type deduction system</a></dt><dt>7. <a href="ar01s07.html">Practical considerations</a></dt><dd><dl><dt>7.1. <a href="ar01s07.html#id2827024">Performance</a></dt><dt>7.2. <a href="ar01s07.html#id2827515">About compiling</a></dt><dt>7.3. <a href="ar01s07.html#id2827576">Portability</a></dt></dl></dd><dt>8. <a href="ar01s08.html">Relation to other Boost libraries</a></dt><dd><dl><dt>8.1. <a href="ar01s08.html#id2827965">Boost Function</a></dt><dt>8.2. <a href="ar01s08.html#id2828068">Boost Bind</a></dt></dl></dd><dt>9. <a href="ar01s09.html">Contributors</a></dt><dt>A. <a href="apa.html">Rationale for some of the design decisions</a></dt><dd><dl><dt>1. <a href="apa.html#sect:why_weak_arity">
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Lambda functor arity
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</a></dt></dl></dd><dt><a href="bi01.html">Bibliography</a></dt></dl></div><a href="lambda_docs_as_one_file.html" target="_top">Documentation as a one big HTML-file</a><div class="section"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="introduction"></a>1. In a nutshell</h2></div></div><p>
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The Boost Lambda Library (BLL in the sequel) is a C++ template
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library, which implements form of <span class="emphasis"><i>lambda abstractions</i></span> for C++.
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The term originates from functional programming and lambda calculus, where a lambda abstraction defines an unnamed function.
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The primary motivation for the BLL is to provide flexible and
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convenient means to define unnamed function objects for STL algorithms.
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In explaining what the library is about, a line of code says more than a thousand words; the
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following line outputs the elements of some STL container
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<tt>a</tt> separated by spaces:
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<pre class="programlisting">for_each(a.begin(), a.end(), std::cout << _1 << ' ');</pre>
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The expression <tt>std::cout << _1 << ' '</tt> defines a unary function object.
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The variable <tt>_1</tt> is the parameter of this function, a <span class="emphasis"><i>placeholder</i></span> for the actual argument.
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Within each iteration of <tt>for_each</tt>, the function is
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called with an element of <tt>a</tt> as the actual argument.
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This actual argument is substituted for the placeholder, and the “body” of the function is evaluated.
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</p><p>The essence of BLL is letting you define small unnamed function objects, such as the one above, directly on the call site of an STL algorithm.
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</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="ar01s02.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"> </td><td width="20%" align="center"> </td><td width="40%" align="right" valign="top"> 2. Getting Started</td></tr></table></div></body></html>
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