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<div><h2 class="title">
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<a name="variadic_macro_data"></a>Chapter 1. The Variadic Macro Data Library 1.10</h2></div>
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<div><div class="author"><h3 class="author">
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<span class="firstname">Edward</span> <span class="surname">Diener</span>
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<div><p class="copyright">Copyright © 2010-2017 Tropic Software
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East Inc</p></div>
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<div class="toc">
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<p><b>Table of Contents</b></p>
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<dl class="toc">
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<dt><span class="section"><a href="index.html#variadic_macro_data.vmd_intro">Introduction</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_naming.html">Naming conventions</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_whyhow.html">Why and how to use</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_vmacros.html">Using variadic macros</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_vc.html">Visual C++ define</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_detail.html">Functional groups</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_data_types.html">Data types</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic.html">Macros for working
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with data types</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic.html#variadic_macro_data.vmd_specific_generic.vmd_specific">Specific
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macros for working with data types</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic.html#variadic_macro_data.vmd_specific_generic.vmd_specific.vmd_test_empty">Emptiness</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic.html#variadic_macro_data.vmd_specific_generic.vmd_specific.vmd_constraints">Macro
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constraints</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic.html#variadic_macro_data.vmd_specific_generic.vmd_specific.vmd_identifier">Identifiers</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic.html#variadic_macro_data.vmd_specific_generic.vmd_specific.vmd_number">Numbers</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic.html#variadic_macro_data.vmd_specific_generic.vmd_specific.vmd_type">Types</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic.html#variadic_macro_data.vmd_specific_generic.vmd_specific.vmd_pp_data_types">VMD
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and Boost PP data types</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic.html#variadic_macro_data.vmd_specific_generic.vmd_specific.vmd_identifying">Identifying
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macros and BOOST_VMD_IS_EMPTY</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic.html#variadic_macro_data.vmd_specific_generic.vmd_specific.vmd_sptable">Summing
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up the specific VMD macros</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic/vmd_generic.html">Generic
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macros for working with data types</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic/vmd_generic.html#variadic_macro_data.vmd_specific_generic.vmd_generic.vmd_sequence">Parsing
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sequences</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic/vmd_generic.html#variadic_macro_data.vmd_specific_generic.vmd_generic.vmd_sequence.vmd_sequence_convert">Converting
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sequences</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic/vmd_generic.html#variadic_macro_data.vmd_specific_generic.vmd_generic.vmd_sequence.vmd_sequence_access">Accessing
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a sequence element</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic/vmd_generic/vmd_convert_sequence.html">Getting
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the type of data</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic/vmd_generic/vmd_equality.html">Testing
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for equality and inequality</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_specific_generic/vmd_generic/vmd_gnctable.html">Summing
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up the generic macros</a></span></dt>
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</dl></dd>
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</dl></dd>
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<dt><span class="section"><a href="variadic_macro_data/vmd_modifiers.html">Macros with modifiers</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="variadic_macro_data/vmd_modifiers.html#variadic_macro_data.vmd_modifiers.vmd_modifiers_return_type">Return
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type modifiers</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_modifiers/vmd_modifiers_filter.html">Filtering
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modifiers</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_modifiers/vmd_modifiers_identifier.html">Identifier
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modifiers</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_modifiers/vmd_modifiers_splitting.html">Splitting
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modifiers</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_modifiers/vmd_modifiers_index.html">Index
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modifiers</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_modifiers/vmd_modifiers_single.html">Modifiers
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and the single-element sequence</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="variadic_macro_data/vmd_identifier_subtype.html">Identifier
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subtypes</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_useful.html">Useful variadic macros
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not in Boost PP</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="variadic_macro_data/vmd_useful.html#variadic_macro_data.vmd_useful.vmd_assert">Asserting
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and data types</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_useful/vmd_identity.html">Generating
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emptiness and identity</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_useful/vmd_empty_ppdata.html">Functionality
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for "empty" seqs and tuples</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="variadic_macro_data/vmd_internal_macro.html">Controlling internal
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||
usage</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_reentrant.html">Boost PP re-entrant
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versions</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_dynamic_typing.html">Input as dynamic
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types</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_vc_isms.html">Visual C++ gotchas in
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VMD</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_conv.html">Version 1.7 to 1.8 conversion</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data/vmd_examples.html">Examples using VMD functionality</a></span></dt>
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<dt><span class="section"><a href="variadic_macro_data_reference.html">Variadic Macro Data Reference</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="variadic_macro_data_reference.html#header.boost.vmd.assert_hpp">Header <boost/vmd/assert.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/assert_is_array_hpp.html">Header <boost/vmd/assert_is_array.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/assert_is_empty_hpp.html">Header <boost/vmd/assert_is_empty.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/assert_is_identifier_hpp.html">Header <boost/vmd/assert_is_identifier.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/assert_is_list_hpp.html">Header <boost/vmd/assert_is_list.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/assert_is_number_hpp.html">Header <boost/vmd/assert_is_number.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/assert_is_seq_hpp.html">Header <boost/vmd/assert_is_seq.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/assert_is_tuple_hpp.html">Header <boost/vmd/assert_is_tuple.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/assert_is_type_hpp.html">Header <boost/vmd/assert_is_type.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/elem_hpp.html">Header <boost/vmd/elem.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/empty_hpp.html">Header <boost/vmd/empty.hpp></a></span></dt>
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<dd><dl></dl></dd>
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||
<dt><span class="section"><a href="header/boost/vmd/enum_hpp.html">Header <boost/vmd/enum.hpp></a></span></dt>
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<dd><dl></dl></dd>
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||
<dt><span class="section"><a href="header/boost/vmd/equal_hpp.html">Header <boost/vmd/equal.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
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||
<dt><span class="section"><a href="header/boost/vmd/get_type_hpp.html">Header <boost/vmd/get_type.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/identity_hpp.html">Header <boost/vmd/identity.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/is_array_hpp.html">Header <boost/vmd/is_array.hpp></a></span></dt>
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<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/is_empty_hpp.html">Header <boost/vmd/is_empty.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/is_empty_array_hpp.html">Header <boost/vmd/is_empty_array.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/is_empty_list_hpp.html">Header <boost/vmd/is_empty_list.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
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||
<dt><span class="section"><a href="header/boost/vmd/is_general_identifier_hpp.html">Header <boost/vmd/is_general_identifier.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
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||
<dt><span class="section"><a href="header/boost/vmd/is_identifier_hpp.html">Header <boost/vmd/is_identifier.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/is_list_hpp.html">Header <boost/vmd/is_list.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/is_multi_hpp.html">Header <boost/vmd/is_multi.hpp></a></span></dt>
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<dd><dl></dl></dd>
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||
<dt><span class="section"><a href="header/boost/vmd/is_number_hpp.html">Header <boost/vmd/is_number.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
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||
<dt><span class="section"><a href="header/boost/vmd/is_parens_empty_hpp.html">Header <boost/vmd/is_parens_empty.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
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||
<dt><span class="section"><a href="header/boost/vmd/is_seq_hpp.html">Header <boost/vmd/is_seq.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/is_tuple_hpp.html">Header <boost/vmd/is_tuple.hpp></a></span></dt>
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<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/is_type_hpp.html">Header <boost/vmd/is_type.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/is_unary_hpp.html">Header <boost/vmd/is_unary.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/not_equal_hpp.html">Header <boost/vmd/not_equal.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/seq/is_vmd_seq_hpp.html">Header <boost/vmd/seq/is_vmd_seq.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/seq/pop_back_hpp.html">Header <boost/vmd/seq/pop_back.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/tuple/pop_back_hpp.html">Header <boost/vmd/tuple/pop_back.hpp></a></span></dt>
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<dd><dl></dl></dd>
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<dt><span class="section"><a href="header/boost/vmd/seq/pop_front_hpp.html">Header <boost/vmd/seq/pop_front.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
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<dt><span class="section"><a href="header/boost/vmd/tuple/pop_front_hpp.html">Header <boost/vmd/tuple/pop_front.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/seq/push_back_hpp.html">Header <boost/vmd/seq/push_back.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
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<dt><span class="section"><a href="header/boost/vmd/tuple/push_back_hpp.html">Header <boost/vmd/tuple/push_back.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/seq/push_front_hpp.html">Header <boost/vmd/seq/push_front.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/tuple/push_front_hpp.html">Header <boost/vmd/tuple/push_front.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/seq/remove_hpp.html">Header <boost/vmd/seq/remove.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/tuple/remove_hpp.html">Header <boost/vmd/tuple/remove.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/size_hpp.html">Header <boost/vmd/size.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/seq/size_hpp.html">Header <boost/vmd/seq/size.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/tuple/size_hpp.html">Header <boost/vmd/tuple/size.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/to_array_hpp.html">Header <boost/vmd/to_array.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/seq/to_array_hpp.html">Header <boost/vmd/seq/to_array.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/tuple/to_array_hpp.html">Header <boost/vmd/tuple/to_array.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/to_list_hpp.html">Header <boost/vmd/to_list.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/seq/to_list_hpp.html">Header <boost/vmd/seq/to_list.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/tuple/to_list_hpp.html">Header <boost/vmd/tuple/to_list.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/to_seq_hpp.html">Header <boost/vmd/to_seq.hpp></a></span></dt>
|
||
<dd><dl></dl></dd>
|
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<dt><span class="section"><a href="header/boost/vmd/array/to_seq_hpp.html">Header <boost/vmd/array/to_seq.hpp></a></span></dt>
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||
<dd><dl></dl></dd>
|
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<dt><span class="section"><a href="header/boost/vmd/list/to_seq_hpp.html">Header <boost/vmd/list/to_seq.hpp></a></span></dt>
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<dd><dl></dl></dd>
|
||
<dt><span class="section"><a href="header/boost/vmd/tuple/to_seq_hpp.html">Header <boost/vmd/tuple/to_seq.hpp></a></span></dt>
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<dd><dl></dl></dd>
|
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<dt><span class="section"><a href="header/boost/vmd/to_tuple_hpp.html">Header <boost/vmd/to_tuple.hpp></a></span></dt>
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<dd><dl></dl></dd>
|
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<dt><span class="section"><a href="header/boost/vmd/array/to_tuple_hpp.html">Header <boost/vmd/array/to_tuple.hpp></a></span></dt>
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<dd><dl></dl></dd>
|
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<dt><span class="section"><a href="header/boost/vmd/list/to_tuple_hpp.html">Header <boost/vmd/list/to_tuple.hpp></a></span></dt>
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<dd><dl></dl></dd>
|
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<dt><span class="section"><a href="header/boost/vmd/seq/to_tuple_hpp.html">Header <boost/vmd/seq/to_tuple.hpp></a></span></dt>
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<dd><dl></dl></dd>
|
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<dt><span class="section"><a href="header/boost/vmd/tuple/is_vmd_tuple_hpp.html">Header <boost/vmd/tuple/is_vmd_tuple.hpp></a></span></dt>
|
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<dd><dl></dl></dd>
|
||
</dl></dd>
|
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<dt><span class="section"><a href="variadic_macro_data/vmd_design.html">Design</a></span></dt>
|
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<dt><span class="section"><a href="variadic_macro_data/vmd_compilers.html">Compilers</a></span></dt>
|
||
<dt><span class="section"><a href="variadic_macro_data/vmd_history.html">History</a></span></dt>
|
||
<dt><span class="section"><a href="variadic_macro_data/vmd_ack.html">Acknowledgements</a></span></dt>
|
||
<dt><span class="section"><a href="index/s23.html">Index</a></span></dt>
|
||
</dl>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||
<a name="variadic_macro_data.vmd_intro"></a><a class="link" href="index.html#variadic_macro_data.vmd_intro" title="Introduction">Introduction</a>
|
||
</h2></div></div></div>
|
||
<p>
|
||
Welcome to the Variadic Macro Data library.
|
||
</p>
|
||
<p>
|
||
The Variadic Macro Data library, referred to hereafter as VMD for short, is
|
||
a library of variadic macros which provide enhancements to the functionality
|
||
in the Boost preprocessor library ( Boost PP ), especially as it relates to
|
||
preprocessor data types.
|
||
</p>
|
||
<p>
|
||
In the Boost PP library the preprocessor data types which have specific functionality
|
||
are numbers ( values between 0 and BOOST_PP_LIMIT_MAG) and the composite data
|
||
types Boost PP arrays, Boost PP lists, Boost PP seqs, and Boost PP tuples.
|
||
</p>
|
||
<p>
|
||
The preprocessor data types with which VMD has specific functionality are the
|
||
same data types as the Boost PP library as well as these other preprocessor
|
||
data types: emptiness, VMD identifiers, VMD types ( a subset of identifiers
|
||
), and VMD sequences, which is another composite data type. A sequence is zero
|
||
or more of any of the other preprocessor data types, other than emptiness,
|
||
which have been previously mentioned and supported by the VMD library, sequentially
|
||
following each other.
|
||
</p>
|
||
<p>
|
||
The VMD library does not replicate in any way the functionality of the Boost
|
||
PP data types, but does extend some of that functionality in various ways,
|
||
along with also providing specific functionality for emptiness, VMD identifiers,
|
||
VMD types, and VMD sequences.
|
||
</p>
|
||
<h4>
|
||
<a name="variadic_macro_data.vmd_intro.h0"></a>
|
||
<span class="phrase"><a name="variadic_macro_data.vmd_intro.data_type_examples"></a></span><a class="link" href="index.html#variadic_macro_data.vmd_intro.data_type_examples">Data
|
||
type examples</a>
|
||
</h4>
|
||
<div class="table">
|
||
<a name="variadic_macro_data.vmd_intro.dwe"></a><p class="title"><b>Table 1.1. Data types with examples</b></p>
|
||
<div class="table-contents"><table class="table" summary="Data types with examples">
|
||
<colgroup>
|
||
<col>
|
||
<col>
|
||
</colgroup>
|
||
<thead><tr>
|
||
<th>
|
||
<p>
|
||
Type
|
||
</p>
|
||
</th>
|
||
<th>
|
||
<p>
|
||
Example
|
||
</p>
|
||
</th>
|
||
</tr></thead>
|
||
<tbody>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
identifier
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
anyname
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
number
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
47
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
type
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
BOOST_VMD_TYPE_NUMBER
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
array
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
(4,(an_identifier,156,BOOST_VMD_TYPE_IDENTIFIER))
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
list
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
(78,(some_identifier,(BOOST_VMD_TYPE_TYPE,BOOST_PP_NIL)))
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
seq
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
(identifier)(89)(245)
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
tuple
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
(any_id,175,BOOST_VMD_TYPE_LIST,happy,21)
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
sequence
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
tree 59 (56,BOOST_VMD_TYPE_SEQ) (128)(fire)(clown) (47,(BOOST_VMD_TYPE_TUPLE,BOOST_PP_NIL))
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
</tbody>
|
||
</table></div>
|
||
</div>
|
||
<br class="table-break"><h4>
|
||
<a name="variadic_macro_data.vmd_intro.h1"></a>
|
||
<span class="phrase"><a name="variadic_macro_data.vmd_intro.emptiness"></a></span><a class="link" href="index.html#variadic_macro_data.vmd_intro.emptiness">Emptiness</a>
|
||
</h4>
|
||
<p>
|
||
Often we speak of a macro expanding to nothing or being passed nothing as an
|
||
argument. Instead of the term "nothing", which can mean many things
|
||
in general in C++ programming terms, we will call this facility of the preprocessor
|
||
"emptiness".
|
||
</p>
|
||
<p>
|
||
Emptiness is the lack of any preprocessing tokens. A macro which expands to
|
||
nothing, as in:
|
||
</p>
|
||
<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">RETURN_NOTHING</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span>
|
||
</pre>
|
||
<p>
|
||
is said to return emptiness. Conversely a macro which could accept nothing
|
||
when invoked, such as in:
|
||
</p>
|
||
<pre class="programlisting"><span class="identifier">RETURN_NOTHING</span><span class="special">()</span>
|
||
</pre>
|
||
<p>
|
||
is said to accept emptiness, or no preprocxessing tokens.
|
||
</p>
|
||
<p>
|
||
Finally emptiness can be part of any composite data type as in:
|
||
</p>
|
||
<pre class="programlisting"><span class="special">(</span><span class="number">45</span><span class="special">,,</span><span class="identifier">some_name</span><span class="special">)</span>
|
||
</pre>
|
||
<p>
|
||
where the second Boost PP tuple element is empty.
|
||
</p>
|
||
<h4>
|
||
<a name="variadic_macro_data.vmd_intro.h2"></a>
|
||
<span class="phrase"><a name="variadic_macro_data.vmd_intro.what_is_the_advantage_to_using_t"></a></span><a class="link" href="index.html#variadic_macro_data.vmd_intro.what_is_the_advantage_to_using_t">What
|
||
is the advantage to using the VMD library ?</a>
|
||
</h4>
|
||
<p>
|
||
In the Boost PP library a good deal of functionality centers upon manipulating
|
||
Boost PP numbers, and particularly the Boost PP numbers of 0 and 1 as a boolean
|
||
value on which you can use Boost PP preprocessing logic to take different preprocessing
|
||
paths when writing a macro. In other words when using Boost PP the logic of
|
||
a macro is often based on the value of a Boost PP number. This is because Boost
|
||
PP numbers can be compared to each other for equality or inequality, among
|
||
other types of comparison, and Boost PP macros which use this ability to compare
|
||
Boost PP numbers, such as the Boost PP macros BOOST_PP_IF or BOOST_PP_IIF,
|
||
can choose different macro expansion paths based on the results of such a comparison.
|
||
</p>
|
||
<p>
|
||
The Boost VMD library adds to the comparison of Boost PP numbers the ability
|
||
to compare any of its other data types for equality or inequality, therefore
|
||
allowing the logic of a macro to depend on the value of any of the preprocessor
|
||
data types it supports.
|
||
</p>
|
||
<p>
|
||
Even more signficantly the Boost VMD library has the ability to discover the
|
||
type of preprocessing data if that data is one of the data types the VMD library
|
||
supports, which gives the end-user not only the ability to change the macro
|
||
expansion logic based on the value of a supported data type but also based
|
||
on the actual type of preprocessing data.
|
||
</p>
|
||
<p>
|
||
The ability to determining macro expansion based on the type of a macro argument
|
||
allows the macro programmer to create a single macro which expands differently
|
||
based on the type of preprocessing data of one or more of its arguments, as
|
||
well as the value of an argument of a particular type. This allows macro logic
|
||
to be designed in a more flexible way, relying on the type of data and/or the
|
||
value of the data. If this intrigues you, continue reading to understand how
|
||
you can use VMD to do macro programming.
|
||
</p>
|
||
<h4>
|
||
<a name="variadic_macro_data.vmd_intro.h3"></a>
|
||
<span class="phrase"><a name="variadic_macro_data.vmd_intro.functionality_areas"></a></span><a class="link" href="index.html#variadic_macro_data.vmd_intro.functionality_areas">Functionality
|
||
areas</a>
|
||
</h4>
|
||
<p>
|
||
The functionality of the library may be summed up as:
|
||
</p>
|
||
<div class="orderedlist"><ol class="orderedlist" type="1">
|
||
<li class="listitem">
|
||
Provide a better way of testing for and using empty parameters and empty
|
||
preprocessor data.
|
||
</li>
|
||
<li class="listitem">
|
||
Provide ways for testing/parsing for VMD identifiers, Boost PP numbers,
|
||
VMD types, Boost PP tuples, Boost PP arrays, Boost PP lists, and Boost
|
||
PP seqs.
|
||
</li>
|
||
<li class="listitem">
|
||
Provide ways for testing/parsing VMD sequences of VMD identifiers, Boost
|
||
PP numbers, VMD types, Boost PP tuples, Boost PP arrays, Boost PP lists,
|
||
and Boost PP seqs.
|
||
</li>
|
||
<li class="listitem">
|
||
Provide some useful variadic only macros not in Boost PP.
|
||
</li>
|
||
</ol></div>
|
||
<p>
|
||
The library is a header only library and all macros in the library are included
|
||
by a single header, whose name is 'vmd.hpp'. Individual headers may be used
|
||
for different functionality in the library and will be denoted when that functionality
|
||
is explained.
|
||
</p>
|
||
<p>
|
||
All the macros in the library begin with the sequence 'BOOST_VMD_' to distinguish
|
||
them from other macros the end-user might use. Therefore the end-user should
|
||
not use any C++ identifiers, whether in macros or otherwise, which being with
|
||
the sequence 'BOOST_VMD_'.
|
||
</p>
|
||
<p>
|
||
Use of the library is only dependent on Boost PP. The library also uses Boost
|
||
detail lightweight_test.hpp for its own tests.
|
||
</p>
|
||
</div>
|
||
</div>
|
||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||
<td align="left"><p><small>Last revised: April 13, 2021 at 16:25:07 GMT</small></p></td>
|
||
<td align="right"><div class="copyright-footer"></div></td>
|
||
</tr></table>
|
||
<hr>
|
||
<div class="spirit-nav"><a accesskey="n" href="variadic_macro_data/vmd_naming.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a></div>
|
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</body>
|
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|