Support for zero length arrays

[SVN r34154]

array0.cpp

@@ -0,0 +1,107 @@
+/* tests for using class array<> specialization for size 0
+ * (C) Copyright Alisdair Meredith 2006.
+ * Distributed under the Boost Software License, Version 1.0. (See
+ * accompanying file LICENSE_1_0.txt or copy at
+ * http://www.boost.org/LICENSE_1_0.txt)
+ */
+
+#include <string>
+#include <iostream>
+#include <boost/array.hpp>
+
+namespace {
+unsigned int failed_tests = 0;
+
+void    fail_test( const char * reason ) {
+    ++failed_tests;
+    std::cerr << "Test failure " << failed_tests << ": " << reason << std::endl;
+}
+
+template< class T >
+void    BadValue( const T &  )
+{
+    fail_test( "Unexpected value" );
+}
+
+template< class T >
+void    RunTests()
+{
+    typedef boost::array< T, 0 >    test_type;
+
+    //  Test value and aggegrate initialization
+    test_type                   test_case   =   {};
+    const boost::array< T, 0 >  const_test_case = test_type();
+
+    test_case.assign( T() );
+
+    //  front/back and operator[] must compile, but calling them is undefined
+    //  Likewise, all tests below should evaluate to false, avoiding undefined behaviour
+    if( !test_case.empty() ) {
+        BadValue( test_case.front() );
+    }
+
+    if( !const_test_case.empty() ) {
+        BadValue( const_test_case.back() );
+    }
+
+    if( test_case.size() > 0 ) {
+        BadValue( test_case[ 0 ] );
+    }
+
+    if( const_test_case.max_size() > 0 ) {
+        BadValue( const_test_case[ 0 ] );
+    }
+
+    //  Assert requirements of TR1 6.2.2.4
+    if( test_case.begin() != test_case.end() ) {
+        fail_test( "Not an empty range" );
+    }
+    if( const_test_case.begin() != const_test_case.end() ) {
+        fail_test( "Not an empty range" );
+    }
+
+    if( test_case.begin() == const_test_case.begin() ) {
+        fail_test( "iterators for different containers are not distinct" );
+    }
+
+    if( test_case.data() == const_test_case.data() ) {
+    //  Value of data is unspecified in TR1, so no requirement this test pass or fail
+    //  However, it must compile!
+    }
+
+
+    //  Check can safely use all iterator types with std algorithms
+    std::for_each( test_case.begin(), test_case.end(), BadValue< T > );
+    std::for_each( test_case.rbegin(), test_case.rend(), BadValue< T > );
+    std::for_each( const_test_case.begin(), const_test_case.end(), BadValue< T > );
+    std::for_each( const_test_case.rbegin(), const_test_case.rend(), BadValue< T > );
+
+    //  Check swap is well formed
+    std::swap( test_case, test_case );
+
+    //  Check assigment operator and overloads are well formed
+    test_case   =   const_test_case;
+
+    //  Confirm at() throws the std lib defined exception
+    try {
+        BadValue( test_case.at( 0 ) );
+    } catch ( const std::range_error & ) {
+    }
+
+    try {
+        BadValue( const_test_case.at( 0 ) );
+    } catch ( const std::range_error & ) {
+    }
+}
+
+}
+
+int main()
+{
+    RunTests< bool >();
+    RunTests< void * >();
+    RunTests< long double >();
+    RunTests< std::string >();
+    return failed_tests;
+}
+

include/boost/array.hpp

@@ -135,6 +135,7 @@ namespace boost {
 
         // direct access to data (read-only)
         const T* data() const { return elems; }
+        T* data() { return elems; }
 
         // use array as C array (direct read/write access to data)
         T* c_array() { return elems; }
@@ -161,6 +162,120 @@ namespace boost {
 
     };
 
+    template< class T >
+    class array< T, 0 > {
+
+      public:
+        // type definitions
+        typedef T              value_type;
+        typedef T*             iterator;
+        typedef const T*       const_iterator;
+        typedef T&             reference;
+        typedef const T&       const_reference;
+        typedef std::size_t    size_type;
+        typedef std::ptrdiff_t difference_type;
+
+        // iterator support
+        iterator begin() { return iterator( reinterpret_cast< T * >( this ) ); }
+        const_iterator begin() const { return const_iterator(  reinterpret_cast< const T * >( this ) ); }
+        iterator end() { return begin(); }
+        const_iterator end() const { return begin(); }
+
+        // reverse iterator support
+#if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION) && !defined(BOOST_MSVC_STD_ITERATOR) && !defined(BOOST_NO_STD_ITERATOR_TRAITS)
+        typedef std::reverse_iterator<iterator> reverse_iterator;
+        typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
+#elif defined(_MSC_VER) && (_MSC_VER == 1300) && defined(BOOST_DINKUMWARE_STDLIB) && (BOOST_DINKUMWARE_STDLIB == 310)
+        // workaround for broken reverse_iterator in VC7
+        typedef std::reverse_iterator<std::_Ptrit<value_type, difference_type, iterator,
+                                      reference, iterator, reference> > reverse_iterator;
+        typedef std::reverse_iterator<std::_Ptrit<value_type, difference_type, const_iterator,
+                                      const_reference, iterator, reference> > const_reverse_iterator;
+#else
+        // workaround for broken reverse_iterator implementations
+        typedef std::reverse_iterator<iterator,T> reverse_iterator;
+        typedef std::reverse_iterator<const_iterator,T> const_reverse_iterator;
+#endif
+
+        reverse_iterator rbegin() { return reverse_iterator(end()); }
+        const_reverse_iterator rbegin() const {
+            return const_reverse_iterator(end());
+        }
+        reverse_iterator rend() { return reverse_iterator(begin()); }
+        const_reverse_iterator rend() const {
+            return const_reverse_iterator(begin());
+        }
+
+        // operator[]
+        reference operator[](size_type i)
+        {
+            BOOST_ASSERT( "out of range" );
+            failed_rangecheck();
+        }
+
+        const_reference operator[](size_type i) const
+        {
+            BOOST_ASSERT( "out of range" );
+            failed_rangecheck();
+        }
+
+        // at() with range check
+        reference at(size_type i)               {   failed_rangecheck();  }
+        const_reference at(size_type i) const   {   failed_rangecheck();  }
+
+        // front() and back()
+        reference front()
+        {
+            failed_rangecheck();
+        }
+
+        const_reference front() const
+        {
+            failed_rangecheck();
+        }
+
+        reference back()
+        {
+            failed_rangecheck();
+        }
+
+        const_reference back() const
+        {
+            failed_rangecheck();
+        }
+
+        // size is constant
+        static size_type size() { return 0; }
+        static bool empty() { return true; }
+        static size_type max_size() { return 0; }
+        enum { static_size = 0 };
+
+        void swap (array<T,0>& y) {
+        }
+
+        // direct access to data (read-only)
+        const T* data() const { return 0; }
+        T* data() { return 0; }
+
+        // use array as C array (direct read/write access to data)
+        T* c_array() { return 0; }
+
+        // assignment with type conversion
+        template <typename T2>
+        array<T,0>& operator= (const array<T2,0>& ) {
+            return *this;
+        }
+
+        // assign one value to all elements
+        void assign (const T& ) {   }
+
+        // check range (may be private because it is static)
+        static void failed_rangecheck () {
+                throw std::range_error("attempt to access element of an empty array");
+            }
+
+    };
+
     // comparisons
     template<class T, std::size_t N>
     bool operator== (const array<T,N>& x, const array<T,N>& y) {