forked from boostorg/preprocessor
boost.css
[SVN r13956]
This commit is contained in:
Vesa Karvonen
@ -1,9 +1,10 @@
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link rel="stylesheet" type="text/css" href="../../../boost.css">
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<title>Boost.Preprocessor - Tutorial</title>
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</head>
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<body bgcolor="#FFFFFF" link="#0000ff" vlink="#800080">
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<body link="#0000ff" vlink="#800080">
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<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
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"header">
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<tr>
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@ -19,10 +20,10 @@
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<hr>
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<h2>Contents</h2>
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<dl>
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<dl class="page-index">
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<dt><a href="#Motivation">Motivation</a></dt>
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<dt><a href="#Techniques">Preprocessor Metaprogramming Techniques</a>
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<dl>
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<dl class="page-index">
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<dt><a href="#Local Macro">Use a Local Macro to avoid small scale repetition</a></dt>
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<dt><a href="#UNUSED">Use BOOST_PP_EMPTY as an unused parameter in Local
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Macro instantiations</a></dt>
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@ -53,8 +54,7 @@
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must be overloaded for every distinct number of parameters that is to be supported.
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Example:</p>
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<blockquote>
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<pre>template <class R>
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<pre>template <class R>
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yes_type is_function_tester(R (*)());
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template <class R, class A0>
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yes_type is_function_tester(R (*)(A0));
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@ -65,7 +65,6 @@ yes_type is_function_tester(R (*)(A0, A1, A2));
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// ...
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</pre>
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</blockquote>
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<P>The need for this kind of repetition occurs particularly frequently while implementing
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generic components or metaprogramming facilities, but the need also manifests
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@ -108,15 +107,14 @@ yes_type is_function_tester(R (*)(A0, A1, A2));
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<p>Using the primitives of the PREPROCESSOR library, the is_function_tester()s
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could be implemented like this:</p>
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<blockquote>
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<pre>#define IS_FUNCTION_TESTER(N,_)\
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<pre>#define IS_FUNCTION_TESTER(N,_)\
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template<class R BOOST_PP_COMMA_IF(N) BOOST_PP_ENUM_PARAMS(N, class A)>\
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yes_type is_function_tester(R (*)(BOOST_PP_ENUM_PARAMS(N,A)));
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BOOST_PP_REPEAT_2ND(BOOST_PP_INC(MAX_IS_FUNCTION_TESTER_PARAMS),IS_FUNCTION_TESTER,_)
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#undef IS_FUNCTION_TESTER
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</pre>
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</blockquote>
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<p>In order to change the maximum number of function parameters supported, you
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now simply change the MAX_IS_FUNCTION_TESTER_PARAMS definition and recompile.</p>
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<HR>
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@ -128,8 +126,7 @@ BOOST_PP_REPEAT_2ND(BOOST_PP_INC(MAX_IS_FUNCTION_TESTER_PARAMS),IS_FUNCTION_TEST
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<P><B><a name="Local Macro"></a><a href="examples_preprocessed.htm#Local Macro">EXAMPLE</a>:</B>
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Use a Local Macro to avoid small scale repetition</P>
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<blockquote>
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<pre>#define BOOST_PP_DEF(OP) \
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<pre>#define BOOST_PP_DEF(OP) \
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template<class T, int n> \
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vec<T,n>& \
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operator OP##= \
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@ -149,7 +146,6 @@ BOOST_PP_DEF(*)
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BOOST_PP_DEF(/)
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#undef BOOST_PP_DEF
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</pre>
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</blockquote>
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<P><B>TIP:</B> It is usually okay to use a standard macro name like BOOST_PP_DEF
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for this kind of code, because the macro is both defined and undefined in the
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@ -167,8 +163,7 @@ the line continuation operator when they are aligned.</P>
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<P><B><a name="UNUSED"></a><a href="examples_preprocessed.htm#UNUSED">EXAMPLE</a>:</B>
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Use BOOST_PP_EMPTY as an unused parameter in Local Macro instantiations</P>
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<blockquote>
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<pre>#define BOOST_PP_DEF(CV) \
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<pre>#define BOOST_PP_DEF(CV) \
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template<class base> \
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CV() typename implement_subscript_using_begin_subscript<base>::value_type&\
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implement_subscript_using_begin_subscript<base>::operator[]\
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@ -182,7 +177,6 @@ BOOST_PP_DEF(BOOST_PP_EMPTY)
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BOOST_PP_DEF(const BOOST_PP_EMPTY)
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#undef BOOST_PP_DEF
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</pre>
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</blockquote>
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<P><B>HOW:</B> BOOST_PP_EMPTY() expands to nothing and can be used as
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an unused parameter.</P>
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@ -206,8 +200,7 @@ of the line continuation operators without making the code too unreadable.</P>
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<HR>
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<P><a name="CAT"></a><a href="examples_preprocessed.htm#CAT"><B>EXAMPLE:</B></a> Use BOOST_PP_CAT instead of ## when necessary</P>
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<blockquote>
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<pre>#define STATIC_ASSERT(EXPR)\
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<pre>#define STATIC_ASSERT(EXPR)\
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enum\
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{ BOOST_PP_CAT(static_check_,__LINE__) = (EXPR) ? 1 : -1\
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};\
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@ -220,22 +213,21 @@ of the line continuation operators without making the code too unreadable.</P>
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STATIC_ASSERT(sizeof(int) <= sizeof(long));
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</pre>
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</blockquote>
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<P><B>WHY:</B> Macro expansion proceeds recursively in "layers". Token pasting
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prevents the preprocessor from performing macro expansion, therefore it
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is often necessary to delay token concatenation.</P>
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<hr>
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<p><a name="STRINGIZE"></a><a href="examples_preprocessed.htm#STRINGIZE"><B>EXAMPLE:</B></a> Use BOOST_PP_STRINGIZE instead of # whenever necessary</p>
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<blockquote>
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<pre>#define NOTE(STR)\
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<pre>#define NOTE(STR)\
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message(__FILE__ "(" BOOST_PP_STRINGIZE(__LINE__) ") : " STR)
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// ...
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#pragma NOTE("TBD!")
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</pre>
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</blockquote>
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<p><b>WHY:</b> Macro expansion proceeds recursively in "layers". Stringization
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prevents the preprocessor from performing macro expansion, therefore it is often
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necessary to delay stringization.</p>
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@ -251,8 +243,8 @@ STATIC_ASSERT(sizeof(int) <= sizeof(long));
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<li> BOOST_PP_COMMA_IF</li>
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</ul>
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<p>to avoid O(N) repetition on lists in general</p>
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<blockquote>
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<pre>struct make_type_list_end;
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<pre>struct make_type_list_end;
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template
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< BOOST_PP_ENUM_PARAMS_WITH_A_DEFAULT
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@ -290,12 +282,10 @@ public:
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>::type type;
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};
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</pre>
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</blockquote>
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<P><B>HOW:</B> BOOST_PP_REPEAT uses simulated recursion (pseudo code):</P>
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<blockquote>
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<pre>#define BOOST_PP_REPEAT(N,M,P) BOOST_PP_REPEAT##N(M,P)
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<pre>#define BOOST_PP_REPEAT(N,M,P) BOOST_PP_REPEAT##N(M,P)
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#define BOOST_PP_REPEAT0(M,P)
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#define BOOST_PP_REPEAT1(M,P) M(0,P)
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#define BOOST_PP_REPEAT2(M,P) M(0,P) M(1,P)
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@ -303,7 +293,6 @@ public:
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#define BOOST_PP_REPEAT4(M,P) BOOST_PP_REPEAT3(M,P) M(3,P)
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// ...
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</pre>
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</blockquote>
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<P>BOOST_PP_ENUM_PARAMS variations use BOOST_PP_REPEAT</P>
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@ -318,12 +307,10 @@ public:
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enable user configuration of code repetition based on need rather than some
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"reasonable" upper limit</P>
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<blockquote>
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<pre>#ifndef MAKE_TYPE_LIST_MAX_LENGTH
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<pre>#ifndef MAKE_TYPE_LIST_MAX_LENGTH
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#define MAKE_TYPE_LIST_MAX_LENGTH 8
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#endif
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</pre>
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</blockquote>
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<P>Now the user can configure the make_type_list primitive without modifying library
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code.</P>
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@ -332,8 +319,7 @@ enable user configuration of code repetition based on need rather than some
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Use BOOST_PP_REPEAT and a Token Look-Up Function to eliminate categorical
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repetition</P>
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<blockquote>
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<pre>// CAVEAT: My compiler is not standard on arithmetic types.
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<pre>// CAVEAT: My compiler is not standard on arithmetic types.
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#define ARITHMETIC_TYPE(I) ARITHMETIC_TYPE##I
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#define ARITHMETIC_TYPE0 bool
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#define ARITHMETIC_TYPE1 char
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@ -366,7 +352,6 @@ BOOST_PP_REPEAT
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// ...
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</pre>
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</blockquote>
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<P><B>NOTE:</B> The repetition of the above
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example can be eliminated using template metaprogramming <A href="bibliography.htm#[Czarnecki]">[Czarnecki]</A> as well. However
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@ -376,8 +361,7 @@ using template metaprogramming.</P>
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<P><B><a name="2ND_REPEAT"></a><a href="examples_preprocessed.htm#2ND_REPEAT">EXAMPLE</a>:</B>
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Use BOOST_PP_REPEAT_2ND to avoid O(N*N) repetition</P>
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<blockquote>
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<pre>#ifndef MAX_VEC_ARG_CNT
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<pre>#ifndef MAX_VEC_ARG_CNT
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#define MAX_VEC_ARG_CNT 8
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#endif
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@ -403,8 +387,6 @@ BOOST_PP_REPEAT_2ND
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// ...
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</pre>
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</blockquote>
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<P><B>HOW:</B> BOOST_PP_REPEAT_2ND is implemented separately, so it
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is possible to combine BOOST_PP_REPEAT and BOOST_PP_REPEAT_2ND.</P>
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@ -412,14 +394,12 @@ BOOST_PP_REPEAT_2ND
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<P><a name="IF"></a><a href="examples_preprocessed.htm#IF"><B>EXAMPLE:</B></a> Use BOOST_PP_IF to implement special case for the first element</P>
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<blockquote>
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<pre>#define BOOST_PP_COMMA_IF(C)\
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<pre>#define BOOST_PP_COMMA_IF(C)\
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BOOST_PP_IF(C,BOOST_PP_COMMA,BOOST_PP_EMPTY)()
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BOOST_PP_IF(0,true,false) == false;
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BOOST_PP_IF(1,true,false) == true;
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</pre>
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</blockquote>
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<P>BOOST_PP_IF enables convenient generation of lists using BOOST_PP_REPEAT.</P>
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@ -428,28 +408,27 @@ BOOST_PP_IF(1,true,false) == true;
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you have to make the other parameter a function-like macro, too. This can often
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be done using BOOST_PP_IDENTITY. Consider the following example (by
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Aleksey Gurtovoy):</P>
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<blockquote>
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<pre>#define NUMBERED_EXPRESSION(I,X)\
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<pre>#define NUMBERED_EXPRESSION(I,X)\
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BOOST_PP_IF \
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( I \
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, BOOST_PP_IDENTITY(X##I) \
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, BOOST_PP_EMPTY \
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)()</pre>
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</blockquote>
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<P><b>NOTE:</b> Like in the above implementation of COMMA_IF, the result of IF
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is often invoked and not the THEN and ELSE parameters. If the parameters were
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invoked, the code would not expand correctly, because the EMPTY parameter would
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get expanded to nothing before the IF would be properly expanded.</P>
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<P><b>HOW:</b> BOOST_PP_IF is defined for the entire repeat range (pseudo
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code):</P>
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<blockquote>
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<pre>#define BOOST_PP_IF(C,THEN,ELSE) BOOST_PP_IF##C(THEN,ELSE)
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<pre>#define BOOST_PP_IF(C,THEN,ELSE) BOOST_PP_IF##C(THEN,ELSE)
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#define BOOST_PP_IF0(THEN,ELSE) ELSE
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#define BOOST_PP_IF1(THEN,ELSE) THEN
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#define BOOST_PP_IF2(THEN,ELSE) THEN
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// ...
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</pre>
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</blockquote>
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<hr>
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@ -461,8 +440,7 @@ comparison operations on decimal integer literals in the range [0,BOOST_PP_LIMIT
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<p>Suppose that you want to generate a numbered lists with a special element inserted
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at a desired position. For example: E0, E1, S, E2. Consider the following example:</p>
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<blockquote>
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<pre>#define SPECIAL_NUMBERED_LIST(N,I,ELEM,SPECIAL)\
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<pre>#define SPECIAL_NUMBERED_LIST(N,I,ELEM,SPECIAL)\
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BOOST_PP_ASSERT_MSG(BOOST_PP_LESS(I,N),BAD PARAMS FOR SPECIAL_NUMBERED_LIST!)\
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BOOST_PP_ENUM_PARAMS(I,ELEM)\
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BOOST_PP_COMMA_IF(I) SPECIAL\
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@ -483,7 +461,6 @@ SPECIAL_NUMBERED_LIST(3,1,E,S)
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SPECIAL_NUMBERED_LIST(3,2,E,S)
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SPECIAL_NUMBERED_LIST(3,3,E,S)
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</pre>
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</blockquote>
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<hr>
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<p>Revised
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@ -492,9 +469,9 @@ SPECIAL_NUMBERED_LIST(3,3,E,S)
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</p>
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<p><i>© Copyright <a href="http://www.housemarque.com">Housemarque Oy</a> 2002</i></p>
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<p><i>Permission to copy, use, modify, sell and distribute this document is granted
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<p>Permission to copy, use, modify, sell and distribute this document is granted
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provided this copyright notice appears in all copies. This document is provided
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"as is" without express or implied warranty, and with no claim as to its suitability
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for any purpose.</i></p>
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for any purpose.</p>
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</body>
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</html>
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