From 7c8a3d04b79affaf9a4e932ca015ca6f2bacdea4 Mon Sep 17 00:00:00 2001
From: Jeremy Siek <jeremy.siek@gmail.com>
Date: Sun, 29 Oct 2000 21:53:41 +0000
Subject: [PATCH] removed cruft

[SVN r8065]
---
 concept_checking.html | 286 ------------------------------------------
 1 file changed, 286 deletions(-)

diff --git a/concept_checking.html b/concept_checking.html
index ce970ae..82451a9 100644
--- a/concept_checking.html
+++ b/concept_checking.html
@@ -905,292 +905,6 @@ organization of the STL concepts, upon which these concept checks
 are based. Thanks to Boost members for helpful comments and
 reviews.
 
-<!----
-
-
-To provide better diagnostics, the user's error needs to be caught
-earlier, at the top of the <tt>std::stable_sort()</tt> function.  As
-mentioned in D&amp;E[<a
-href="./bibliography.html#stroustrup94:_design_evolution">2</a>], the
-error can be caught by exercising all of the requirements needed by
-the template function. Exactly how the requirements are exercised is a
-tricky issue, since we want the code to be compiled but not executed
-at run time. The solution we use is to exercise the requirements in a
-separate function, and then assign the function to a function pointer.
-This causes the compiler to instantiate the function without actually
-invoking the function. Additionally, the pointer assignment can be
-categorized as ``dead code'' and removed by optimizing compilers.  The
-following code shows how this technique can be applied to the
-<tt>std::stable_sort()</tt> function.
-
-<pre>
-  template &lt;class RandomAccessIterator&gt;
-  void stable_sort_constraints(RandomAccessIterator i) {
-    typedef typename std::iterator_traits&lt;RandomAccessIterator&gt;
-      ::value_type T;
-    const T a, b;
-    bool r = a &lt; b; // make sure less-than operator is defined
-    ...
-  }
-
-  template &lt;class RandomAccessIterator&gt;
-  void stable_sort(RandomAccessIterator first,
-                   RandomAccessIterator last) {
-    typedef void (*fptr_type)(RandomAccessIterator);
-    fptr_type x = &stable_sort_constraints;
-    ...
-  }
-</pre>
-
-Many times there is a large set of requirements that need to be
-checked, and it would be cumbersome for the library implementor to
-write a constraints function like <tt>stable_sort_constraints()</tt>
-for every public function. The solution to this is to group
-requirements together in pre-defined constraint functions, which can
-then be used at the top of template functions. The C++ standard and
-the <a href="http://www.sgi.com/Technology/STL">SGI STL
-documentation</a> already define a large number of standard
-requirement groups, called <i>concepts</i>, and these concepts are
-used to document the requirements for the standard generic
-algorithms. The SGI STL implementation now includes constraint
-functions for each of these concepts, and uses the functions to check
-the template arguments of its algorithms.
-
-<p>
-There is a concept <a
-href="http://www.sgi.com/Technology/STL/LessThanComparable.html">
-LessThanComparable</a> that we can use to check the parameters of
-<tt>stable_sort()</tt>. The constraints function for this concept is
-shown below. The constraint function is written as a member function
-to provide a convenient place to define the objects involved in the
-expressions without accidentally adding requirements about the
-objects' constructors. The expressions within the
-<tt>constraints()</tt> function correspond to the <i>valid
-expressions</i> section of the concept documentation. Typedefs can also
-be added to enforce the <i>associated types</i> of the concept.
-
-<pre>
-  template &lt;class T&gt;
-  struct LessThanComparable_concept
-  {
-    void constraints() {
-      // require comparison operators returning bool
-      r = a &lt; b || a &gt; b || a &lt;= b || a &gt;= b;
-    }
-    T a, b;
-    bool r;
-  };
-</pre>
-
-To make it easy for the library implementor to invoke the concept
-checks, we wrap the function pointer mechanism in a macro named
-<tt>REQUIRE</tt>. The following code snippet shows how to use
-<tt>REQUIRE</tt> to make sure that the value type of the iterator is
-<a href="http://www.sgi.com/Technology/STL/LessThanComparable.html">
-LessThanComparable</a>}.
-
-<pre>
-  template &lt;class RandomAccessIterator&gt;
-  void stable_sort(RandomAccessIterator first,
-                   RandomAccessIterator last) {
-    typedef typename std::iterator_traits&lt;RandomAccessIterator&gt;
-      ::value_type ValueType;
-    REQUIRE(ValueType, LessThanComparable);
-    ...
-  }
-</pre>
-
-The definition of <tt>REQUIRE</tt> macro is shown below. The macro
-makes sure that the <tt>type_var</tt> is a type that models the
-<tt>concept</tt>. The macro creates a member function pointer to the
-<tt>constraints()</tt> function of the given concept checking class,
-which has been instantiated with <tt>type_var</tt>. The macro then
-assigns the pointer to itself to avoid warnings about unused
-variables. Finally, we wrap this in a do-while loop to prevent name
-clashes. The <tt>##</tt> is the preprocessor's concatenation
-operator. Here it is used to append the suffix <tt>_concept</tt> to
-the concept name.
-
-<pre>
-#define REQUIRE(type_var, concept)                              \
-do {                                                            \
-  void (concept##_concept &lt;type_var&gt;::*x)() =                   \
-    BOOST_FPTR concept##_concept &lt;type_var&gt;::constraints;       \
-  x = x; } while (0)
-</pre>
-
-The macro <tt>BOOST_FPTR</tt> is there to handle a portability
-problem. Some compilers require the use of &amp; to get the address of
-a function, others don't.
-
-<pre>
-#if defined(__GNUC__) || defined(__KCC) || defined(__ghs)
-#define BOOST_FPTR &
-#else
-#define BOOST_FPTR
-#endif
-</pre>
-
-It is also desirable to check the template arguments to classes,
-however the <tt>REQUIRE</tt> macro can not be used inside the body of
-a class declaration since consists of statements. Also, it is not a
-good idea to use <tt>REQUIRE</tt> in the constructors (or any other
-members of a class) because this does not ensure that the concept
-checks will be compiled. To solve this problem a variation on the
-function pointer technique is used. A nested class template is created
-whose template parameter is a function pointer (yes, this is legal
-C++). The nested class is then instantiated (by using it in a typedef)
-with a pointer to the appropriate <tt>constraints()</tt> member
-function. We use the <tt>type_var</tt> and <tt>concept</tt> names in
-the name of the nested class template to guard against name clashes
-with other concept checks in the same class. The following gives the
-definition of the <tt>CLASS_REQUIRES</tt> macro.
-
-<pre>
-#define CLASS_REQUIRES(type_var, concept)                                       \
-  typedef void (concept##_concept &lt;type_var&gt;::* func##type_var##concept)();     \
-  template &lt;func##type_var##concept _Tp1&gt;                                       \
-  struct dummy_struct_##type_var##concept { };                                  \
-  typedef dummy_struct_##type_var##concept&lt;                                     \
-    BOOST_FPTR concept##_concept &lt;type_var&gt;::constraints&gt;                       \
-    dummy_typedef_##type_var##concept
-</pre>
-
-<tt>CLASS_REQUIRES</tt> was not used in the implementation of the STL
-concept checks because only a few compilers support using function
-pointers in class template parameters.
-
-
--->
-
-
-
-
-
-<!--
-
-
-<P>
-The C++ language does not provide direct support for ensuring that
-template arguments meet the requirements demanded of them by the
-generic algorithm or template class. This means that if the user makes
-an error, the resulting compiler error will point to somewhere deep
-inside the implementation of the generic algorithm, giving an error
-that may not be easy to match with the cause.
-
-<P>
-We have developed a method for forcing the compiler to give better
-error messages. The idea is to exercise all the requirements placed on
-the template arguments at the very beginning of the generic algorithm.
-We have created some macros and a methodology for how to do this.
-
-<P>
-Suppose we wish to add concept checks to the STL <a
-href="http://www.sgi.com/Technology/STL/copy.html"><TT>copy()</TT></a>
-algorithm, which has the following prototype.
-<PRE>
-  template &lt;class InIter, class OutIter&gt;
-  OutIter copy(InIter first, InIter last, OutIter result);
-</PRE>
-We will need to make sure the <TT>InIter</TT> is a model of <a
-href="http://www.sgi.com/Technology/STL/InputIterator.html">InputIterator</a>
-and that <TT>OutIter</TT> is a model of <a
-href="http://www.sgi.com/Technology/STL/OutputIterator.html">OutputIterator</a>. The
-first step is to create the code that will exercise the expressions
-associated with each of these concepts.  The following is the concept
-checking class for <a
-href="http://www.sgi.com/Technology/STL/OutputIterator.html">OutputIterator</a>.
-The iterator objects <TT>i</TT> and <TT>j</TT> are data members of the
-concept checking class which would normally require the <TT>Iter</TT>
-type to be <a
-href="http://www.sgi.com/Technology/STL/DefaultConstructible.html">DefaultConstructible</a>. However,
-we never create instances of concept checking classes so this
-requirement is not induced.
-
-<P>
-<PRE>
-  template &lt;class Iter&gt;
-  struct OutputIterator {
-    CLASS_REQUIRES(Iter, Assignable);
-    void constraints() {
-      (void)*i;        // require dereference operator
-      ++i;             // require preincrement operator
-      i++;             // require postincrement operator
-      *i++ = *j;       // require postincrement and assignment
-    }
-    Iter i, j;
-  };
-</PRE>
-
-<P>
-Once the concept checking classes are complete, one simply needs to
-invoke them at the beginning of the generic algorithm using our
-<TT>REQUIRE</TT> macro. Here's what the STL <TT>copy()</TT> algorithm
-looks like with the concept checks inserted.
-
-<P>
-<PRE>
-  template &lt;class InIter, class OutIter&gt;
-  OutIter copy(InIter first, InIter last, OutIter result)
-  { 
-    REQUIRE(OutIter, OutputIterator); 
-    REQUIRE(InIter, InputIterator); 
-    return copy_aux(first, last, result, VALUE_TYPE(first)); 
-  }
-</PRE>
-
-<P>
-Looking back at the <TT>OutputIterator</TT> concept checking class, you
-might wonder why we used the <TT>CLASS_REQUIRES</TT> macro instead of
-just <TT>REQUIRE</TT>. The reason for this is that different tricks are
-needed to force compilation of the checking code when invoking the
-macro from inside a class definition instead of a function.
-
-<P>
-For the most part, the user does not need to know how to create
-concept checks and insert them in generic algorithms, however it is
-good to know what they are. This will make the error messages coming
-from libraries that use concept checks easier to understand. Also if
-you are unsure about whether you can use a certain class with a
-particular algorithm, or whether some custom-made class of your own is
-compatible, a good first check is to invoke the appropriate concept
-checker.
-
-<P>
-Here's a quick example program that one could write to see if the
-types <a
-href="../graph/docs/adjacency_list.html"><TT>adjacency_list</TT></a> and <a
-href="../graph/docs/edge_list.html"><TT>edge_list</TT></a> really model the
-concepts they claim to.
-
-<P>
-<PRE>
-  #include &lt;boost/graph/graph_concepts.hpp&gt;
-  #include &lt;boost/graph/adjacency_list.hpp&gt;
-  #include &lt;boost/graph/edge_list.hpp&gt;
-
-  using namespace boost;
-
-  int main(int,char*[])
-  {
-    typedef adjacency_list&lt;listS,vecS,bidirectionalS&gt; AdjList;
-    REQUIRE(AdjList, VertexAndEdgeListGraph);
-    REQUIRE(AdjList, BidirectionalGraph);
-
-    typedef std::pair&lt;int, int&gt; E;
-    typedef edge_list&lt;E*, E, int&gt; EdgeList;
-    REQUIRE(EdgeList, EdgeListGraph);
-
-    return 0;
-  }
-</PRE>
-
-<P>
-If you create your own generic algorithms we highly encourage you to use
-and publish the corresponding concept checks.
-
--->
-
 <br>
 <HR>
 <TABLE>