diff options
Diffstat (limited to 'libstdc++-v3/docs/html/ext/pb_assoc/ms_gen.html')
| -rw-r--r-- | libstdc++-v3/docs/html/ext/pb_assoc/ms_gen.html | 440 |
1 files changed, 0 insertions, 440 deletions
diff --git a/libstdc++-v3/docs/html/ext/pb_assoc/ms_gen.html b/libstdc++-v3/docs/html/ext/pb_assoc/ms_gen.html deleted file mode 100644 index 468c121a70b..00000000000 --- a/libstdc++-v3/docs/html/ext/pb_assoc/ms_gen.html +++ /dev/null @@ -1,440 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> -<html> - <head> - <title>Mapping-Semantics Genericity</title> - <meta name="GENERATOR" content="Microsoft Visual Studio .NET 7.1"> - <meta name="vs_targetSchema" content="http://schemas.microsoft.com/intellisense/ie5"> - </head> -<body bgcolor = "white"> - - -<h1>Mapping-Semantics</h1> - -<p> - This section describes genericity over different mapping-semantics. It is organized as follows. -</p> -<ol> - <li><a href = "#intro">Introduction</a></li> - <li><a href = "#ds_policy">Data Types as a Policy</a></li> - <li><a href = "#problem">The Basic Problem</a></li> - <li><a href = "#mapping_level">Mapping Levels</a></li> - <li><a href = "#ms_traits">Tags and Traits</a></li> - <li><a href = "#drawbacks">Drawbacks</a></li> -</ol> - - -<h2><a name = "intro">Introduction</a></h2> - -<p> -<a href = "motivation.html#mapping_semantics">Motivation::Mapping Semantics</a> discussed scalability issues with the STL's non-unique-mapping associative containers; non-unique association inherently embeds linked-lists in associative containers resulting in scalability problems and other problems. -</p> - -<p> - In <tt>pb_assoc</tt>, all containers have unique-key semantics. Each key is uniquely mapped to "something". -</p> - - -<h2><a name = "ds_policy">Data Types as a Policy</a></h2> - -<p> - All associative-containers in <tt>pb_assoc</tt> are parameterized by a data type. -<i>E.g.,</i> <a href = "cc_hash_assoc_cntnr.html">cc_hash_assoc_cntnr</a> is parameterized as -</p> -<pre> -<b>template</b>< - <b>typename</b> Key, - <b>typename</b> Data, - ...> -<b>class</b> <a href = "cc_hash_assoc_cntnr.html">cc_hash_assoc_cntnr</a>; -</pre> - -<p> - There are no separate classes for maps, sets, multimaps, and multisets (as the STL has). Rather, the mapping-semantic is set by specifying the <tt>Key</tt> parameter. -</p> - -<ol> - <li> If <tt>Data</tt> is any type (<i>e.g.</i>, <tt><b>int</b></tt> or -<tt>std::string</tt>), then the container is a "map" - it maps each <tt>Key</tt> object to a <tt>Data</tt> object. - </li> - <li> If <tt>Data</tt> is -<a href = "null_data_type.html"><tt>null_data_type</tt></a>, -then the container is a "set" - it stores each <tt>Key</tt> object. In this case, each <tt>Key</tt> object is not really mapped to anything (except, implicitly, to the fact that it is stored in the container object). - </li> - <li> - If <tt>Data</tt> is -<a href = "compound_data_type.html">compound_data_type</a><tt><Cntnr></tt>, -then the container is a "multimap" - it maps each <tt>Key</tt> object into a <tt>Cntnr</tt> object. This structure is recursive - <tt>Cntnr</tt> itself can be a "map", "set", "multimap", and so forth. - </li> -</ol> - -<p> - Each container derives from one of the three containers -in the oval of Figure -<a href = "#ms_cd"> -Data-types as a policy -</a>. -</p> - - <ol> - <li><a href = "basic_assoc_cntnr.html"><tt>basic_assoc_cntnr</tt></a> -is the base for most instantiations of a container's <tt>Data</tt> paramter. This -base includes the definition of <tt>data_type</tt>, and supports -<tt><b>operator</b>[]</tt>. - </li> - <li><a href = "basic_assoc_cntnr_no_data.html"><tt>basic_assoc_cntnr</tt></a> is the base for a -<a href = "null_data_type"><tt>null_data_type</tt></a> instantiation of a container's <tt>Data</tt> paramter. This -base lacks the definition of <tt>data_type</tt>, and does not support -<tt><b>operator</b>[]</tt>. - <li><a href = "basic_assoc_cntnr_compound_data.html"><tt>basic_assoc_cntnr</tt></a> is the base for a -<a href = "compound_data_type.html"><tt>compound_data_type</tt></a><tt><Cntnr></tt> instantiation of a container's <tt>Data</tt> paramter. This -base includes the definition of <tt>data_type</tt>, and supports -<tt><b>operator</b>[]</tt>. It further supports some advanced functionality described in the remainder of this section. - </ol> - - -<h6 align = "center"> -<a name = "ms_cd"> -<img src = "ms_cd.jpg" width = "70%" alt = "no image"> -</h6> -</a> -<h6 align = "center"> -Data-types as a policy. -</h6> - - -<h2><a name = "problem">The Basic Problem</a></h2> - -<p> - Consider a <tt>pb_assoc</tt> "multimap" mapping integers to characters. -Since a <tt>pb_assoc</tt> "multimap" is a "map" of "sets", -if <tt>m</tt> is an object of this type, it is not possible to directly use -<tt>m.insert(std::make_pair(2, 'b')</tt> (however, it is possible to directly use -<tt>m[2].insert('b')</tt>). In would be nice if this method whould be supported. -</p> - -<p> - Put differently, while the <tt>pb_assoc</tt> "multimap" can be viewed logically as the collection -</p> -<p> - { <tt><b>int</b></tt> → {<tt><b>char</b></tt>} }, -</p> -<p> - It would be nice if it could simultaneously be viewed as the collection -</p> -<p> - { (<tt><b>int</b></tt>, <tt><b>char</b></tt>) }, -</p> -<p><i>i.e.</i>, a "set" of pairs.</p> - -<p> - In more general terms, it would be nice to be able to simultaneously -view a collection -</p> -<p> -{ key_type_0 → { key_type_1 → { key_type_2 → { key_type_3 → { ... }}}}} -</p> -<p> -as each of the following: -</p> -<p> -{ (key_type_0, key_type_1) → { key_type_2 &rarr { key_type_e → { ... }}}}, -</p> -<p> -{ (key_type_0, key_type_1, key_type_2) &rarr { key_type_3 → { ... }}} -</p> -<p> -{ (key_type_0, key_type_1, key_type_2, key_type_3 ) &rarr { }} -</p> -<p> -... -</p> - - -<p> -<a href = #mapping_level">Mapping_Levels</a> discusses the mechanism -for these multiple views in <tt>pb_assoc</tt> -</p> - - - -<h2><a name = "mapping_level">Mapping Levels</a></h2> - -<p> - Each associative container in <tt>pb_assoc</tt> has -a <i>mapping level</i>. The mapping level is defined by -the instantiation of a container's <tt>Data</tt> -parameter: -</p> - -<ol> - <li> If the <tt>Data</tt> parameter is instantiated -by -<a href = "null_data_type.html"><tt>null_data_type</tt></a> (<i>i.e.</i>, -the container is a "set"), then the mapping level is 1. - </li> - <li> If the <tt>Data</tt> parameter is instantiated -by -<a href = "compound_data_type.html">compound_data_type</a><tt><Cntnr></tt> -(<i>i.e.</i>, the container is a "multimap"), then the mapping level -is 1 + the mapping level of <tt>Cntnr</tt>. - </li> - <li> If the <tt>Data</tt> parameter is instantiated -by any other type, <i>e.g.</i>, <tt><b>char</b></tt> (<i>i.e.</i>, -the container is a "map"), then the mapping level is 1. - </li> -</ol> - -<p> - Containers can be rebound, at compile time, to different mapping levels. -The compound data-type specialization <a href = "basic_assoc_cntnr_compound_data.html"><tt>basic_assoc_cntnr</tt></a> -defines internally -</p> -<pre> -<b>template</b>< - <b>int</b> Mapping_Level> -<b>struct</b> rebind -{ - <b>typedef</b> - ... - other; -}; -</pre> - -<p> -(which is similar to the STL's allocator rebind mechanism). -the type <tt>other</tt> is the view of the container with mapping -level <tt>Mapping_Level</tt>. The container can be safely cast -to <tt>other</tt>. -</p> - -<p> - As an example, consider the type -</p> - -<pre> -<b>typedef</b> - <a href = "cc_hash_assoc_cntnr.html">cc_hash_assoc_cntnr</a>< - <b>int</b>, - <a href = "compound_data_type.html">compound_data_type</a>< - <a href = "tree_assoc_cntnr.html">tree_assoc_cntnr</a>< - <b>char</b>, - <a href = "null_data_type.html"><tt>null_data_type</tt></a>> > > - cntnr_t; -</pre> -<p> - which is a "map" mapping each <tt><b>int</b></tt> to -a "set" of <tt><b>char</b></tt>s. In this case, <tt>cntnr_t</tt> has mapping level 2. -</p> - -<p> - An object of type <tt>cntnr_t</tt> cannot support <tt>insert(std::make_pair(2, 'b'));</tt>. On the other hand, the following code snippet shows how to do so: -</p> - -<pre> -cntnr_t c; - -<b>typedef</b> - t::rebind<1>::other - t_; - -((t_ &)c).insert(std::make_pair(2, 'b')); -</pre> - - -<p> -<a href = "../example/mapping_level_example.cpp"><tt>mapping_level_example.cpp</tt></a> shows a more detailed example. -</p> - - - -<h2><a name = "ms_traits">Tags and Traits</a></h2> - -<p> - It is, of course, beneficial to query types for their mapping semantics. -</p> - -<p> - Each container defines internally the type <tt>ms_category</tt> -as its mapping-semantics tag (hopefully this name is not copyrighted -by some major corporation). The possible tags, shown in Figure - -are the following: -</p> - -<ol> - <li> - <a href = "basic_ms_tag.html"><tt>basic_ms_tag</tt></a> -is a basic mapping-semantics tag. It is the type defined by "set"s. - </li> - <li> - <a href = "data_enabled_ms_tag.html"><tt>data_enabled_ms_tag</tt></a> -is a mapping-semantics tag of types that have data. It is the type defined by "map"s. - </li> - <li> - <a href = "compound_data_enabled_ms_tag.html"><tt>compound_data_enabled_ms_tag</tt></a> -is a mapping-semantics tag of types that have compound data. It is the type defined by "multimap"s. - </li> -</ol> - -<p> - Additionally, a container's mapping semantics can be queried by traits. For any -container <tt>Cntnr</tt>, -</p> - -<pre> -<a href = "ms_traits.html">ms_traits</a><Cntnr>::mapping_level -</pre> - -<p> - indicates the mapping level of the container, for example. -</p> - - - -<h2><a name = "drawbacks">Drawbacks</a></h2> - -<tt>pb_assoc</tt>'s mapping-semantics design has some drawbacks compared to that of the STL. - - -<h3>Equivalent, Non-Identical Keys</h3> - -<p> - The STL's multimaps and multisets allow storing equivalent, non-identical keys -[<a href = "references.html#kleft00sets">kleft00sets</a>]. For example, assume a bank maintains a data structure monitoring the accounts opened by each person. This could be modeled as the following: -</p> - -<pre> -<i>// Name type.</i> -<b>typedef</b> - std::string - name; - -<i>// Account-id type.</i> -<b>typedef</b> - <b>unsigned long</b> - account_id; - -<i>// Association between a name and an account id.</i> -<b>class</b> opened_info -{ -<b>public</b>: - ... - - <i>// Comparison operator.</i> - <b>bool</b> - <b></b>operator<</b> - (<b>const</b> opened_info &r_other) - { - <i>Comparison is defined as the comparison of the names.</i> - <b>return</b> m_name < r_other.m_name; - } - - -<b>private</b>: - name m_name; - - account_id m_acc_id; -}; - -<i>// A multiset of opened accounts.</i> -<b>typedef</b> - std::multiset< - opened_info> - all_opened_info; -</pre> - -<p> - <tt>std::multiset</tt> can accomodate multiple equivalent, non-identical <tt>opened_info</tt> - those with the same name but different account id. -</p> - -<p> - In <tt>pb_assoc</tt>, however, non-unique mapping is unsupported. The equivalent to the above could be -</p> - -<pre> -<b>typedef</b> - tree_assoc_cntnr< - name, - compound_data_type< - cc_hash_assoc_cntnr< - account_id> > > - all_opened_info; -</pre> - -<p> - The drawback lies in the fact that the data stored in -<tt>all_opened_info</tt> is less encapsulated - an <tt>opened_info</tt> -object needs to be constructed when a specific name and account are found, and -an <tt>opened_info</tt> object needs to be decomposed into <tt>name</tt> and -<tt>account_id</tt> objects when it is inserted into a <tt>all_opened_info</tt> -object. -</p> - -<p> - It should be noticed however, that the above drawbacks - construction and decomposition are constant-time additive drawbacks. The drawbacks of the -STL's associative containers are in terms of orders of growth. -</p> - -<h3>Definition of <tt>value_type</tt></h3> - -<p> - The STL's associative containers contain a pleasingly uniform definition of -the <tt>value_type</tt> of a container. -If a container is parameterized by <tt>key</tt> as its <tt>Key</tt>, and <tt>data</tt> as its <tt>Data</tt>, then its <tt>value_type</tt> is -<tt>std::pair<<b>const</b> key, data></tt>; -for example, the <tt>value_type</tt> of <tt>std::map<<b>int</b>, <b>char</b>></tt> is -<tt>std::pair<<b>const int</b>, <b>char</b>></tt>. Futhermore, the <tt>value_type</tt> of a container and the <tt>value_type</tt> of the container's iterators are identical. -</p> - -<p> - In <tt>pb_assoc</tt>, conversely, the rules are more complex. -</p> - -<p> For one, a container's -<tt>value_type</tt> is, in general -<tt>std::pair<<b>const</b> Key, Data></tt>, -but if <tt>Data</tt> is <tt>null_data_type</tt>, then the <tt>value_type</tt> -is -<tt>Key</tt>, -and if -<tt>Data</tt> is -<tt>compound_data_type<Cntnr></tt>, then the <tt>value_type</tt> is -<tt>std::pair<<b>const</b> Key, Cntnr></tt>. -</p> - -<p> - Futhermore, assume that <tt>Cntnr</tt> is an associative container with more than a single mapping level, and let <tt>Cntnr_</tt> be defined as -</p> - -<pre> -<b>typedef</b> - <b>typename</b> Cntnr::<b>template</b> rebind<i>::other</tt> - Cntnr_; -</pre> -<p> -<i>i.e.</i>, the container rebound to a different mapping level. -In this case, the <tt>value_type</tt> of the rebound container is not the <tt>value_type</tt> -of the rebound container's iterators. <i>I.e.</i>, it is <emph>not</emph> true that -<tt><b>typename</b> Cntnr_::value_type</tt> is the same as -<tt><b>typename</b> Cntnr_::iterator::value_type</tt>. This complication never exists for the STL's container. -</p> - -<h6 align = "center"> -<a name = "reference_iterator"> -<img src = "reference_iterator.jpg" width = "70%" alt = "no image"> -</h6> -</a> -<h6 align = "center"> -Iterator of a rebound type. -</h6> - - -<h3>Multisets</h3> - -<p> - <tt>pb_assoc</tt> does not contain a "multiset" type. The closest equivalent is mapping keys to non-negative integral types, <i>e.g.</i>, <tt>size_t</tt>. -</p> - -</body> - -</html> |