Add a constructor from basic_string_view in C++17 or later

Note that we have MrDocs compile as C++17 again (a change that we had
reverted).

CMakeLists.txt

@@ -82,6 +82,9 @@ if (DYNAMIC_BITSET_MRDOCS_BUILD)
     # Create a custom target for MrDocs.
     add_library(dynamic_bitset_mrdocs_target ${TEMP_CPP_FILE})
 
+    # This is to get the documentation of the constructor from basic_string_view.
+    set_target_properties(dynamic_bitset_mrdocs_target PROPERTIES CXX_STANDARD 17 CXX_STANDARD_REQUIRED YES)
+
     # Set any other target properties here.
     target_include_directories(dynamic_bitset_mrdocs_target PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/include")
     target_link_libraries(dynamic_bitset_mrdocs_target PRIVATE boost_dynamic_bitset)

include/boost/dynamic_bitset/config.hpp

@@ -60,4 +60,8 @@ make_non_const( T t )
 #    define BOOST_DYNAMIC_BITSET_SPECIALIZE_STD_HASH
 #endif
 
+#if ( defined( _MSVC_LANG ) && _MSVC_LANG >= 201703L ) || __cplusplus >= 201703L
+#    define BOOST_DYNAMIC_BITSET_USE_CPP17_OR_LATER
+#endif
+
 #endif // include guard

include/boost/dynamic_bitset/dynamic_bitset.hpp

@@ -386,6 +386,27 @@ public:
     template< typename CharT >
     dynamic_bitset( const CharT * s, std::size_t n = std::size_t( -1 ), size_type num_bits = npos, const allocator_type & alloc = allocator_type() );
 
+#if defined( BOOST_DYNAMIC_BITSET_USE_CPP17_OR_LATER )
+
+    //!     Similar to the constructor from a pointer to a C-style
+    //!     string, but takes a `std::basic_string_view`. This
+    //!     constructor is only available if DynamicBitset is compiled
+    //!     as C++17 or later.
+    //!
+    //!     \pre
+    //!     The characters in `sv` are '0' or '1'.
+    //!
+    //!     \param sv The basic_string_view to construct from.
+    //!     \param num_bits The size of the bitset to construct, if
+    //!     different from `npos`. (Otherwise the size of the bitset is
+    //!     `sv.length()`.)
+    //!     \param alloc The allocator to use.
+    // -----------------------------------------------------------------------
+    template< typename CharT, typename Traits >
+    dynamic_bitset( std::basic_string_view< CharT, Traits > sv, size_type num_bits = npos, const allocator_type & alloc = allocator_type() );
+
+#endif
+
     //!     Constructs a bitset from a range of blocks or from an
     //!     integer.
     //!
@@ -1308,7 +1329,7 @@ private:
     void init_from_block_range( BlockIter first, BlockIter last );
 
     template< typename CharT, typename Traits = std::char_traits< CharT > >
-    void init_from_string( const CharT * s, std::size_t pos, std::size_t n, size_type num_bits );
+    void init_from_string( const CharT * s, std::size_t string_length, std::size_t pos, std::size_t n, size_type num_bits );
 
     void init_from_unsigned_long( size_type num_bits, unsigned long value /*,
                                                        const allocator_type& alloc*/

include/boost/dynamic_bitset/impl/dynamic_bitset.ipp

@@ -494,7 +494,7 @@ dynamic_bitset< Block, AllocatorOrContainer >::dynamic_bitset(
 
     : m_bits( alloc ), m_num_bits( 0 )
 {
-    init_from_string( s.c_str(), pos, n, num_bits );
+    init_from_string( s.c_str(), s.length(), pos, n, num_bits );
 }
 
 template< typename Block, typename AllocatorOrContainer >
@@ -506,9 +506,23 @@ dynamic_bitset< Block, AllocatorOrContainer >::dynamic_bitset(
     const allocator_type & alloc )
     : m_bits( alloc ), m_num_bits( 0 )
 {
-    init_from_string( s, 0, n, num_bits );
+    init_from_string( s, std::char_traits< CharT >::length( s ), 0, n, num_bits );
 }
 
+#if defined( BOOST_DYNAMIC_BITSET_USE_CPP17_OR_LATER )
+
+template< typename Block, typename AllocatorOrContainer >
+template< typename CharT, typename Traits >
+dynamic_bitset< Block, AllocatorOrContainer >::dynamic_bitset(
+    std::basic_string_view< CharT, Traits > sv,
+    size_type                               num_bits,
+    const allocator_type &                  alloc )
+    : m_bits( alloc ), m_num_bits( 0 )
+{
+    init_from_string( sv.data(), sv.length(), 0, sv.length(), num_bits );
+}
+
+#endif
 
 template< typename Block, typename AllocatorOrContainer >
 template< typename BlockInputIterator >
@@ -2061,12 +2075,12 @@ template< typename Block, typename AllocatorOrContainer >
 template< typename CharT, typename Traits >
 void
 dynamic_bitset< Block, AllocatorOrContainer >::init_from_string(
-    const CharT * s,
+    const CharT * s,    // caution: not necessarily null-terminated
+    std::size_t   string_length,
     std::size_t   pos,
     std::size_t   n,
     size_type     num_bits )
 {
-    const std::size_t string_length = Traits::length( s );
     BOOST_ASSERT( pos <= string_length );
 
 

test/bitset_test.hpp

@@ -208,6 +208,10 @@ struct bitset_test
         // If M < N, remaining bit positions are zero
         for ( ; j < actual_size; ++j )
             BOOST_TEST( b[ j ] == 0 );
+
+#if defined( BOOST_DYNAMIC_BITSET_USE_CPP17_OR_LATER )
+        BOOST_TEST( Bitset( std::basic_string_view< Ch, Tr >( str ).substr( pos, rlen ), num_bits ) == b );
+#endif
     }
 
     static void