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0323ca1876 | ||
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4227c144de |
@@ -5,7 +5,7 @@
|
||||
The Boost Lambda Library"><link rel="up" href="index.html" title="
|
||||
C++ BOOST
|
||||
|
||||
The Boost Lambda Library"><link rel="previous" href="ar01s09.html" title="9. Contributors"><link rel="next" href="bi01.html" title="Bibliography"></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">A. Rationale for some of the design decisions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ar01s09.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="bi01.html">Next</a></td></tr></table><hr></div><div class="appendix"><h2 class="title" style="clear: both"><a name="id2808832"></a>A. Rationale for some of the design decisions</h2><div class="section"><div class="titlepage"><div><h3 class="title"><a name="sect:why_weak_arity"></a>1.
|
||||
The Boost Lambda Library"><link rel="previous" href="ar01s09.html" title="9. Contributors"><link rel="next" href="bi01.html" title="Bibliography"></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">A. Rationale for some of the design decisions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ar01s09.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="bi01.html">Next</a></td></tr></table><hr></div><div class="appendix"><h2 class="title" style="clear: both"><a name="id2808831"></a>A. Rationale for some of the design decisions</h2><div class="section"><div class="titlepage"><div><h3 class="title"><a name="sect:why_weak_arity"></a>1.
|
||||
Lambda functor arity
|
||||
</h3></div></div><p>
|
||||
The highest placeholder index in a lambda expression determines the arity of the resulting function object.
|
||||
|
||||
@@ -25,7 +25,7 @@ for_each(v.begin(), v.end(), _1 = 1);</pre>
|
||||
Next, we create a container of pointers and make them point to the elements in the first container <tt>v</tt>:
|
||||
|
||||
<pre class="programlisting">
|
||||
list<int*> vp(10);
|
||||
vector<int*> vp(10);
|
||||
transform(v.begin(), v.end(), vp.begin(), &_1);</pre>
|
||||
|
||||
The expression <tt>&_1</tt> creates a function object for getting the address of each element in <tt>v</tt>.
|
||||
|
||||
@@ -533,7 +533,7 @@ By using <tt>var</tt> to make <tt>index</tt> a lambda expression, we get the des
|
||||
In sum, <tt>var(x)</tt> creates a nullary lambda functor,
|
||||
which stores a reference to the variable <tt>x</tt>.
|
||||
When the lambda functor is invoked, a reference to <tt>x</tt> is returned.
|
||||
</p><div class="simplesect"><div class="titlepage"><div><h4 class="title"><a name="id2804083"></a>Naming delayed constants and variables</h4></div></div><p>
|
||||
</p><div class="simplesect"><div class="titlepage"><div><h4 class="title"><a name="id2804084"></a>Naming delayed constants and variables</h4></div></div><p>
|
||||
It is possible to predefine and name a delayed variable or constant outside a lambda expression.
|
||||
The templates <tt>var_type</tt>, <tt>constant_type</tt>
|
||||
and <tt>constant_ref_type</tt> serve for this purpose.
|
||||
@@ -635,13 +635,7 @@ for_each(a, a+5,
|
||||
The BLL supports an alternative syntax for control expressions, suggested
|
||||
by Joel de Guzmann.
|
||||
By overloading the <tt>operator[]</tt> we can
|
||||
get a closer resemblance with the built-in control structures.
|
||||
For example, using this syntax the <tt>if_then</tt> example above
|
||||
can be written as:
|
||||
<pre class="programlisting">
|
||||
for_each(a.begin(), a.end(),
|
||||
if(_1 % 2 == 0)[ cout << _1 ])
|
||||
</pre>
|
||||
get a closer resemblance with the built-in control structures:
|
||||
|
||||
<pre class="programlisting">
|
||||
if_(condition)[then_part]
|
||||
@@ -651,6 +645,13 @@ do_[body].while_(condition)
|
||||
for_(init, condition, increment)[body]
|
||||
</pre>
|
||||
|
||||
For example, using this syntax the <tt>if_then</tt> example above
|
||||
can be written as:
|
||||
<pre class="programlisting">
|
||||
for_each(a.begin(), a.end(),
|
||||
if(_1 % 2 == 0)[ cout << _1 ])
|
||||
</pre>
|
||||
|
||||
As more experience is gained, we may end up deprecating one or the other
|
||||
of these syntaces.
|
||||
|
||||
@@ -975,7 +976,7 @@ int nested(const F& f) {
|
||||
}
|
||||
</pre>
|
||||
|
||||
</p></div><div class="section"><div class="titlepage"><div><h5 class="title"><a name="id2805743"></a>5.9.1.2. Protect</h5></div></div><p>
|
||||
</p></div><div class="section"><div class="titlepage"><div><h5 class="title"><a name="id2805742"></a>5.9.1.2. Protect</h5></div></div><p>
|
||||
The <tt>protect</tt> function is related to unlambda.
|
||||
|
||||
It is also used to prevent the argument substitution taking place,
|
||||
@@ -1109,7 +1110,7 @@ int count = 0;
|
||||
for_each(a.begin(), a.end(),
|
||||
if_then(ll_dynamic_cast<derived*>(_1), ++var(count)));
|
||||
</pre>
|
||||
</p></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2806151"></a>5.10.2. Sizeof and typeid</h4></div></div><p>
|
||||
</p></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2806150"></a>5.10.2. Sizeof and typeid</h4></div></div><p>
|
||||
The BLL counterparts for these expressions are named
|
||||
<tt>ll_sizeof</tt> and <tt>ll_typeid</tt>.
|
||||
|
||||
|
||||
@@ -5,7 +5,7 @@
|
||||
The Boost Lambda Library"><link rel="up" href="index.html" title="
|
||||
C++ BOOST
|
||||
|
||||
The Boost Lambda Library"><link rel="previous" href="ar01s06.html" title="6. Extending return type deduction system"><link rel="next" href="ar01s08.html" title="8. Relation to other Boost libraries"></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">7. Practical considerations</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ar01s06.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ar01s08.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2807558"></a>7. Practical considerations</h2></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2807564"></a>7.1. Performance</h3></div></div><p>In theory, all overhead of using STL algorithms and lambda functors
|
||||
The Boost Lambda Library"><link rel="previous" href="ar01s06.html" title="6. Extending return type deduction system"><link rel="next" href="ar01s08.html" title="8. Relation to other Boost libraries"></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">7. Practical considerations</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ar01s06.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ar01s08.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2807557"></a>7. Practical considerations</h2></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2807564"></a>7.1. Performance</h3></div></div><p>In theory, all overhead of using STL algorithms and lambda functors
|
||||
compared to hand written loops can be optimized away, just as the overhead
|
||||
from standard STL function objects and binders can.
|
||||
|
||||
@@ -97,7 +97,7 @@ The running times are expressed in arbitrary units." border="1"><colgroup><col><
|
||||
</p><p>Some additional performance testing with an earlier version of the
|
||||
library is described
|
||||
[<a href="bi01.html#cit:jarvi:00" title="[Jär00]">Jär00</a>].
|
||||
</p></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2808057"></a>7.2. About compiling</h3></div></div><p>The BLL uses templates rather heavily, performing numerous recursive instantiations of the same templates.
|
||||
</p></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2808056"></a>7.2. About compiling</h3></div></div><p>The BLL uses templates rather heavily, performing numerous recursive instantiations of the same templates.
|
||||
This has (at least) three implications:
|
||||
<div class="itemizedlist"><ul type="disc"><li><p>
|
||||
While it is possible to write incredibly complex lambda expressions, it probably isn't a good idea.
|
||||
|
||||
@@ -5,7 +5,7 @@
|
||||
The Boost Lambda Library"><link rel="up" href="index.html" title="
|
||||
C++ BOOST
|
||||
|
||||
The Boost Lambda Library"><link rel="previous" href="ar01s07.html" title="7. Practical considerations"><link rel="next" href="ar01s09.html" title="9. Contributors"></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">8. Relation to other Boost libraries</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ar01s07.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ar01s09.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2808502"></a>8. Relation to other Boost libraries</h2></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2808510"></a>8.1. Boost Function</h3></div></div><p>Sometimes it is convenient to store lambda functors in variables.
|
||||
The Boost Lambda Library"><link rel="previous" href="ar01s07.html" title="7. Practical considerations"><link rel="next" href="ar01s09.html" title="9. Contributors"></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">8. Relation to other Boost libraries</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ar01s07.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ar01s09.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2808502"></a>8. Relation to other Boost libraries</h2></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2808509"></a>8.1. Boost Function</h3></div></div><p>Sometimes it is convenient to store lambda functors in variables.
|
||||
However, the types of even the simplest lambda functors are long and unwieldy, and it is in general unfeasible to declare variables with lambda functor types.
|
||||
<span class="emphasis"><i>The Boost Function library</i></span> [<a href="bi01.html#cit:boost::function" title="[function]">function</a>] defines wrappers for arbitrary function objects, for example
|
||||
lambda functors; and these wrappers have types that are easy to type out.
|
||||
@@ -13,14 +13,14 @@ lambda functors; and these wrappers have types that are easy to type out.
|
||||
For example:
|
||||
|
||||
<pre class="programlisting">
|
||||
boost::function<int, int, int> f = _1 + _2;
|
||||
boost::function<int&, int&> g = unlambda(_1 += 10);
|
||||
boost::function<int(int, int)> f = _1 + _2;
|
||||
boost::function<int&(int&)> g = (_1 += 10);
|
||||
int i = 1, j = 2;
|
||||
f(i); // returns 3
|
||||
g(i); // sets i to = 11;
|
||||
</pre>
|
||||
|
||||
The return and parameter types of the wrapped function object must be written explicilty as template arguments to the wrapper template <tt>boost::function</tt>; even when lambda functors, which otherwise have generic parameters, are wrapped.
|
||||
The return and parameter types of the wrapped function object must be written explicilty as the template argument to the wrapper template <tt>boost::function</tt>; even when lambda functors, which otherwise have generic parameters, are wrapped.
|
||||
Wrapping a function object with <tt>boost::function</tt> introduces a performance cost comparable to virtual function dispatch, though virtual functions are not actually used.
|
||||
|
||||
Note that storing lambda functors inside <tt>boost::function</tt>
|
||||
@@ -38,13 +38,13 @@ For example:
|
||||
<pre class="programlisting">
|
||||
int* sum = new int();
|
||||
*sum = 0;
|
||||
boost::function<int&, int> counter = *sum += _1;
|
||||
boost::function<int&(int)> counter = *sum += _1;
|
||||
counter(5); // ok, *sum = 5;
|
||||
delete sum;
|
||||
counter(3); // error, *sum does not exist anymore
|
||||
</pre>
|
||||
|
||||
</p></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2808614"></a>8.2. Boost Bind</h3></div></div><p>
|
||||
</p></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2808613"></a>8.2. Boost Bind</h3></div></div><p>
|
||||
<span class="emphasis"><i>The Boost Bind</i></span> [<a href="bi01.html#cit:boost::bind" title="[bind]">bind</a>] library has partially overlapping functionality with the BLL.
|
||||
Basically, the Boost Bind library (BB in the sequel) implements the bind expression part of BLL.
|
||||
There are, however, some semantical differerences.
|
||||
|
||||
@@ -5,7 +5,7 @@
|
||||
The Boost Lambda Library"><link rel="up" href="index.html" title="
|
||||
C++ BOOST
|
||||
|
||||
The Boost Lambda Library"><link rel="previous" href="apa.html" title="A. Rationale for some of the design decisions"></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">Bibliography</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="apa.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> </td></tr></table><hr></div><div id="id2808984" class="bibliography"><div class="titlepage"><div><h2 class="title"><a name="id2808984"></a>Bibliography</h2></div></div><div class="biblioentry"><a name="cit:stepanov:94"></a><p>[STL94] <span class="authorgroup">A. A. Stepanov and M. Lee. </span><span class="title"><I>The Standard Template Library</I>. </span><span class="orgname">Hewlett-Packard Laboratories. </span><span class="pubdate">1994. </span><span class="bibliomisc">
|
||||
The Boost Lambda Library"><link rel="previous" href="apa.html" title="A. Rationale for some of the design decisions"></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">Bibliography</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="apa.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> </td></tr></table><hr></div><div id="id2808983" class="bibliography"><div class="titlepage"><div><h2 class="title"><a name="id2808983"></a>Bibliography</h2></div></div><div class="biblioentry"><a name="cit:stepanov:94"></a><p>[STL94] <span class="authorgroup">A. A. Stepanov and M. Lee. </span><span class="title"><I>The Standard Template Library</I>. </span><span class="orgname">Hewlett-Packard Laboratories. </span><span class="pubdate">1994. </span><span class="bibliomisc">
|
||||
<a href="http://www.hpl.hp.com/techreports" target="_top">www.hpl.hp.com/techreports</a>
|
||||
. </span></p></div><div class="biblioentry"><a name="cit:sgi:02"></a><p>[SGI02] <span class="title"><I>The SGI Standard Template Library</I>. </span><span class="pubdate">2002. </span><span class="bibliomisc"><a href="http://www.sgi.com/tech/stl/" target="_top">www.sgi.com/tech/stl/</a>. </span></p></div><div class="biblioentry"><a name="cit:c++:98"></a><p>[C++98] <span class="title"><I>International Standard, Programming Languages – C++</I>. </span><span class="subtitle">ISO/IEC:14882. </span><span class="pubdate">1998. </span></p></div><div class="biblioentry"><a name="cit:jarvi:99"></a><p>[Jär99] <span class="articleinfo">
|
||||
<span class="author">Jaakko Järvi. </span>
|
||||
|
||||
@@ -444,7 +444,7 @@ Nevertheless, it is straightforward to provide another function template with th
|
||||
Next, we create a container of pointers and make them point to the elements in the first container <literal>v</literal>:
|
||||
|
||||
<programlisting>
|
||||
<![CDATA[list<int*> vp(10);
|
||||
<![CDATA[vector<int*> vp(10);
|
||||
transform(v.begin(), v.end(), vp.begin(), &_1);]]></programlisting>
|
||||
|
||||
The expression <literal><![CDATA[&_1]]></literal> creates a function object for getting the address of each element in <literal>v</literal>.
|
||||
@@ -1578,13 +1578,7 @@ for_each(a, a+5,
|
||||
The BLL supports an alternative syntax for control expressions, suggested
|
||||
by Joel de Guzmann.
|
||||
By overloading the <literal>operator[]</literal> we can
|
||||
get a closer resemblance with the built-in control structures.
|
||||
For example, using this syntax the <literal>if_then</literal> example above
|
||||
can be written as:
|
||||
<programlisting>
|
||||
<![CDATA[for_each(a.begin(), a.end(),
|
||||
if(_1 % 2 == 0)[ cout << _1 ])]]>
|
||||
</programlisting>
|
||||
get a closer resemblance with the built-in control structures:
|
||||
|
||||
<programlisting>
|
||||
<![CDATA[if_(condition)[then_part]
|
||||
@@ -1594,6 +1588,13 @@ do_[body].while_(condition)
|
||||
for_(init, condition, increment)[body]]]>
|
||||
</programlisting>
|
||||
|
||||
For example, using this syntax the <literal>if_then</literal> example above
|
||||
can be written as:
|
||||
<programlisting>
|
||||
<![CDATA[for_each(a.begin(), a.end(),
|
||||
if(_1 % 2 == 0)[ cout << _1 ])]]>
|
||||
</programlisting>
|
||||
|
||||
As more experience is gained, we may end up deprecating one or the other
|
||||
of these syntaces.
|
||||
|
||||
@@ -3029,14 +3030,14 @@ lambda functors; and these wrappers have types that are easy to type out.
|
||||
For example:
|
||||
|
||||
<programlisting>
|
||||
<![CDATA[boost::function<int, int, int> f = _1 + _2;
|
||||
boost::function<int&, int&> g = unlambda(_1 += 10);
|
||||
<![CDATA[boost::function<int(int, int)> f = _1 + _2;
|
||||
boost::function<int&(int&)> g = (_1 += 10);
|
||||
int i = 1, j = 2;
|
||||
f(i); // returns 3
|
||||
g(i); // sets i to = 11;]]>
|
||||
</programlisting>
|
||||
|
||||
The return and parameter types of the wrapped function object must be written explicilty as template arguments to the wrapper template <literal>boost::function</literal>; even when lambda functors, which otherwise have generic parameters, are wrapped.
|
||||
The return and parameter types of the wrapped function object must be written explicilty as the template argument to the wrapper template <literal>boost::function</literal>; even when lambda functors, which otherwise have generic parameters, are wrapped.
|
||||
Wrapping a function object with <literal>boost::function</literal> introduces a performance cost comparable to virtual function dispatch, though virtual functions are not actually used.
|
||||
|
||||
Note that storing lambda functors inside <literal>boost::function</literal>
|
||||
@@ -3054,7 +3055,7 @@ For example:
|
||||
<programlisting>
|
||||
<![CDATA[int* sum = new int();
|
||||
*sum = 0;
|
||||
boost::function<int&, int> counter = *sum += _1;
|
||||
boost::function<int&(int)> counter = *sum += _1;
|
||||
counter(5); // ok, *sum = 5;
|
||||
delete sum;
|
||||
counter(3); // error, *sum does not exist anymore]]>
|
||||
|
||||
@@ -15,7 +15,7 @@
|
||||
The Boost Lambda Library is free software; Permission to copy,
|
||||
use, modify and distribute this software and its documentation is granted, provided this copyright
|
||||
notice appears in all copies.
|
||||
</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#id2790109">Installing the library</a></dt><dt>2.2. <a href="ar01s02.html#id2741935">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#id2741989">Motivation</a></dt><dt>3.2. <a href="ar01s03.html#id2742784">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#id2805476">Special lambda expressions</a></dt><dt>5.10. <a href="ar01s05.html#id2806049">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#id2807564">Performance</a></dt><dt>7.2. <a href="ar01s07.html#id2808057">About compiling</a></dt><dt>7.3. <a href="ar01s07.html#id2808118">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#id2808510">Boost Function</a></dt><dt>8.2. <a href="ar01s08.html#id2808614">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">
|
||||
</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#id2790109">Installing the library</a></dt><dt>2.2. <a href="ar01s02.html#id2741935">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#id2741989">Motivation</a></dt><dt>3.2. <a href="ar01s03.html#id2742784">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#id2805476">Special lambda expressions</a></dt><dt>5.10. <a href="ar01s05.html#id2806049">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#id2807564">Performance</a></dt><dt>7.2. <a href="ar01s07.html#id2808056">About compiling</a></dt><dt>7.3. <a href="ar01s07.html#id2808118">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#id2808509">Boost Function</a></dt><dt>8.2. <a href="ar01s08.html#id2808613">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">
|
||||
Lambda functor arity
|
||||
</a></dt></dl></dd><dt><a href="bi01.html">Bibliography</a></dt></dl></div><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>
|
||||
|
||||
|
||||
@@ -259,7 +259,7 @@ for_each(v.begin(), v.end(), _1 = 1);</pre>
|
||||
Next, we create a container of pointers and make them point to the elements in the first container <tt>v</tt>:
|
||||
|
||||
<pre class="programlisting">
|
||||
list<int*> vp(10);
|
||||
vector<int*> vp(10);
|
||||
transform(v.begin(), v.end(), vp.begin(), &_1);</pre>
|
||||
|
||||
The expression <tt>&_1</tt> creates a function object for getting the address of each element in <tt>v</tt>.
|
||||
@@ -997,7 +997,7 @@ Here is an example of naming a delayed constant:
|
||||
constant_type<char>::type space(constant(' '));
|
||||
for_each(a.begin(),a.end(), cout << space << _1);
|
||||
</pre>
|
||||
</p></div><div class="simplesect"><div class="titlepage"><div><h4 class="title"><a name="id2793531"></a>About assignment and subscript operators</h4></div></div><p>
|
||||
</p></div><div class="simplesect"><div class="titlepage"><div><h4 class="title"><a name="id2793532"></a>About assignment and subscript operators</h4></div></div><p>
|
||||
As described in <a href="#sect:assignment_and_subscript" title="5.2.2. Assignment and subscript operators">Section 5.2.2</a>, assignment and subscripting operators are always defined as member functions.
|
||||
This means, that for expressions of the form
|
||||
<tt>x = y</tt> or <tt>x[y]</tt> to be interpreted as lambda expressions, the left-hand operand <tt>x</tt> must be a lambda expression.
|
||||
@@ -1070,13 +1070,7 @@ for_each(a, a+5,
|
||||
The BLL supports an alternative syntax for control expressions, suggested
|
||||
by Joel de Guzmann.
|
||||
By overloading the <tt>operator[]</tt> we can
|
||||
get a closer resemblance with the built-in control structures.
|
||||
For example, using this syntax the <tt>if_then</tt> example above
|
||||
can be written as:
|
||||
<pre class="programlisting">
|
||||
for_each(a.begin(), a.end(),
|
||||
if(_1 % 2 == 0)[ cout << _1 ])
|
||||
</pre>
|
||||
get a closer resemblance with the built-in control structures:
|
||||
|
||||
<pre class="programlisting">
|
||||
if_(condition)[then_part]
|
||||
@@ -1086,6 +1080,13 @@ do_[body].while_(condition)
|
||||
for_(init, condition, increment)[body]
|
||||
</pre>
|
||||
|
||||
For example, using this syntax the <tt>if_then</tt> example above
|
||||
can be written as:
|
||||
<pre class="programlisting">
|
||||
for_each(a.begin(), a.end(),
|
||||
if(_1 % 2 == 0)[ cout << _1 ])
|
||||
</pre>
|
||||
|
||||
As more experience is gained, we may end up deprecating one or the other
|
||||
of these syntaces.
|
||||
|
||||
@@ -1284,7 +1285,7 @@ objects related to creating and destroying objects,
|
||||
showing the expression to create and call the function object,
|
||||
and the effect of evaluating that expression.
|
||||
|
||||
</p><div class="table"><p><a name="table:constructor_destructor_fos"></a><b>Table 1. Construction and destruction related function objects.</b></p><table summary="Construction and destruction related function objects." border="1"><colgroup><col><col></colgroup><thead><tr><th>Function object call</th><th>Wrapped expression</th></tr></thead><tbody><tr><td><tt>constructor<T>()(<i><tt>arg_list</tt></i>)</tt></td><td>T(<i><tt>arg_list</tt></i>)</td></tr><tr><td><tt>destructor()(a)</tt></td><td><tt>a.~A()</tt>, where <tt>a</tt> is of type <tt>A</tt></td></tr><tr><td><tt>destructor()(pa)</tt></td><td><tt>pa.->A()</tt>, where <tt>pa</tt> is of type <tt>A*</tt></td></tr><tr><td><tt>new_ptr<T>()(<i><tt>arg_list</tt></i>)</tt></td><td><tt>new T(<i><tt>arg_list</tt></i>)</tt></td></tr><tr><td><tt>new_array<T>()(sz)</tt></td><td><tt>new T[sz]</tt></td></tr><tr><td><tt>delete_ptr()(p)</tt></td><td><tt>delete p</tt></td></tr><tr><td><tt>delete_array()(p)</tt></td><td><tt>delete p[]</tt></td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2794800"></a>5.9. Special lambda expressions</h3></div></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2794808"></a>5.9.1. Preventing argument substitution</h4></div></div><p>
|
||||
</p><div class="table"><p><a name="table:constructor_destructor_fos"></a><b>Table 1. Construction and destruction related function objects.</b></p><table summary="Construction and destruction related function objects." border="1"><colgroup><col><col></colgroup><thead><tr><th>Function object call</th><th>Wrapped expression</th></tr></thead><tbody><tr><td><tt>constructor<T>()(<i><tt>arg_list</tt></i>)</tt></td><td>T(<i><tt>arg_list</tt></i>)</td></tr><tr><td><tt>destructor()(a)</tt></td><td><tt>a.~A()</tt>, where <tt>a</tt> is of type <tt>A</tt></td></tr><tr><td><tt>destructor()(pa)</tt></td><td><tt>pa.->A()</tt>, where <tt>pa</tt> is of type <tt>A*</tt></td></tr><tr><td><tt>new_ptr<T>()(<i><tt>arg_list</tt></i>)</tt></td><td><tt>new T(<i><tt>arg_list</tt></i>)</tt></td></tr><tr><td><tt>new_array<T>()(sz)</tt></td><td><tt>new T[sz]</tt></td></tr><tr><td><tt>delete_ptr()(p)</tt></td><td><tt>delete p</tt></td></tr><tr><td><tt>delete_array()(p)</tt></td><td><tt>delete p[]</tt></td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><h3 class="title"><a name="id2794800"></a>5.9. Special lambda expressions</h3></div></div><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2794807"></a>5.9.1. Preventing argument substitution</h4></div></div><p>
|
||||
When a lambda functor is called, the default behavior is to substitute
|
||||
the actual arguments for the placeholders within all subexpressions.
|
||||
|
||||
@@ -1932,7 +1933,7 @@ The BLL works with the following compilers, that is, the compilers are capable o
|
||||
)
|
||||
|
||||
</li></ul></div>
|
||||
</p><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2797482"></a>7.3.1. Test coverage</h4></div></div><p>The following list describes the test files included and the features that each file covers:
|
||||
</p><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2797481"></a>7.3.1. Test coverage</h4></div></div><p>The following list describes the test files included and the features that each file covers:
|
||||
|
||||
<div class="itemizedlist"><ul type="disc"><li><p>
|
||||
<tt>bind_tests_simple.cpp</tt> : Bind expressions of different arities and types of target functions: function pointers, function objects and member functions.
|
||||
@@ -1986,14 +1987,14 @@ lambda functors; and these wrappers have types that are easy to type out.
|
||||
For example:
|
||||
|
||||
<pre class="programlisting">
|
||||
boost::function<int, int, int> f = _1 + _2;
|
||||
boost::function<int&, int&> g = unlambda(_1 += 10);
|
||||
boost::function<int(int, int)> f = _1 + _2;
|
||||
boost::function<int&(int&)> g = (_1 += 10);
|
||||
int i = 1, j = 2;
|
||||
f(i); // returns 3
|
||||
g(i); // sets i to = 11;
|
||||
</pre>
|
||||
|
||||
The return and parameter types of the wrapped function object must be written explicilty as template arguments to the wrapper template <tt>boost::function</tt>; even when lambda functors, which otherwise have generic parameters, are wrapped.
|
||||
The return and parameter types of the wrapped function object must be written explicilty as the template argument to the wrapper template <tt>boost::function</tt>; even when lambda functors, which otherwise have generic parameters, are wrapped.
|
||||
Wrapping a function object with <tt>boost::function</tt> introduces a performance cost comparable to virtual function dispatch, though virtual functions are not actually used.
|
||||
|
||||
Note that storing lambda functors inside <tt>boost::function</tt>
|
||||
@@ -2011,7 +2012,7 @@ For example:
|
||||
<pre class="programlisting">
|
||||
int* sum = new int();
|
||||
*sum = 0;
|
||||
boost::function<int&, int> counter = *sum += _1;
|
||||
boost::function<int&(int)> counter = *sum += _1;
|
||||
counter(5); // ok, *sum = 5;
|
||||
delete sum;
|
||||
counter(3); // error, *sum does not exist anymore
|
||||
@@ -2036,7 +2037,7 @@ a larger set of compilers.
|
||||
</p><p>
|
||||
The following two sections describe what are the semantic differences
|
||||
between the bind expressions in BB and BLL.
|
||||
</p><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2798003"></a>8.2.1. First argument of bind expression</h4></div></div>
|
||||
</p><div class="section"><div class="titlepage"><div><h4 class="title"><a name="id2798002"></a>8.2.1. First argument of bind expression</h4></div></div>
|
||||
|
||||
In BB the first argument of the bind expression, the target function,
|
||||
is treated differently from the other arguments,
|
||||
|
||||
@@ -436,10 +436,10 @@ namespace detail {
|
||||
|
||||
template<class RET, class A, class B>
|
||||
class member_pointer_caller {
|
||||
A a;
|
||||
B b;
|
||||
A a; B b;
|
||||
|
||||
public:
|
||||
member_pointer_caller(A aa, B bb) : a(aa), b(bb) {}
|
||||
member_pointer_caller(const A& aa, const B& bb) : a(aa), b(bb) {}
|
||||
|
||||
RET operator()() const { return (a->*b)(); }
|
||||
|
||||
@@ -589,29 +589,24 @@ struct member_pointer_action_helper<false, true> {
|
||||
|
||||
template<class RET, class A, class B>
|
||||
static RET apply(A& a, B& b) {
|
||||
|
||||
typedef typename ::boost::remove_cv<B>::type plainB;
|
||||
typedef typename detail::member_pointer<plainB>::type ret_t;
|
||||
typedef typename ::boost::remove_cv<A>::type plainA;
|
||||
|
||||
// we always add const (it is just the pointer types, not the types
|
||||
// pointed to) to make the to routes (calling and type deduction)
|
||||
// we always strip cv:s to
|
||||
// make the two routes (calling and type deduction)
|
||||
// to give the same results (and the const does not make any functional
|
||||
// difference)
|
||||
return detail::member_pointer_caller<ret_t, const A&, const B&>(a, b);
|
||||
return detail::member_pointer_caller<ret_t, plainA, plainB>(a, b);
|
||||
}
|
||||
|
||||
template<class A, class B>
|
||||
struct return_type {
|
||||
typedef typename detail::remove_reference_and_cv<B>::type plainB;
|
||||
typedef typename detail::member_pointer<plainB>::type ret_t;
|
||||
typedef typename detail::remove_reference_and_cv<A>::type plainA;
|
||||
|
||||
// we always add const (it is just the pointer types, not the types
|
||||
// pointed to)
|
||||
typedef detail::member_pointer_caller<
|
||||
ret_t,
|
||||
typename boost::add_reference<const A>::type,
|
||||
typename boost::add_reference<const B>::type
|
||||
> type;
|
||||
typedef detail::member_pointer_caller<ret_t, plainA, plainB> type;
|
||||
};
|
||||
};
|
||||
|
||||
@@ -621,17 +616,15 @@ template<> class other_action<member_pointer_action> {
|
||||
public:
|
||||
template<class RET, class A, class B>
|
||||
static RET apply(A& a, B& b) {
|
||||
|
||||
typedef typename
|
||||
::boost::remove_cv<B>::type plainB;
|
||||
|
||||
return
|
||||
detail::member_pointer_action_helper<
|
||||
return detail::member_pointer_action_helper<
|
||||
boost::is_pointer<A>::value &&
|
||||
detail::member_pointer<plainB>::is_data_member,
|
||||
boost::is_pointer<A>::value &&
|
||||
detail::member_pointer<plainB>::is_function_member
|
||||
>::template apply<RET>(a, b);
|
||||
>::template apply<RET>(a, b);
|
||||
}
|
||||
};
|
||||
|
||||
|
||||
Reference in New Issue
Block a user