Add non-standard byte_span() creator functions (issue #3, thanks to @…

…chris0e3)

README.md

@@ -93,6 +93,11 @@ To construct a span from a container with compilers that cannot constrain such a
 
 *span lite* can provide `make_span` creator functions to compensate for the class template argument deduction that is missing from pre-C++17 compilers. See the table below and section [configuration](#configuration).
 
+### `byte_span`
+
+*span lite* can provide `byte_span` creator functions to represent an object as a span of bytes. This requires the C++17 type `std::byte` to be available. See the table below and section [configuration](#configuration).
+
+
 | Kind               | std  | Function or method |                                       
 |--------------------|------|--------------------|
 | **Types**          | | **with_container_t** type to disambiguate below constructors |
@@ -108,10 +113,14 @@ To construct a span from a container with compilers that cannot constrain such a
 | &nbsp; | >= C++11 | template&lt;class T, size_t N><br>constexpr span&lt;const T,N><br>**make_span**(std::array&lt;T,N > const & arr) noexcept |
 | &nbsp; | >= C++11 | template&lt;class Container><br>constexpr auto<br>**make_span**(Container & cont) -><br>&emsp;span&lt;typename Container::value_type> noexcept |
 | &nbsp; | >= C++11 | template&lt;class Container><br>constexpr auto<br>**make_span**(Container const & cont) -><br>&emsp;span&lt;const typename Container::value_type> noexcept |
-| &nbsp; | < C++11  | template&lt;class Container><br>span&lt;typename Container::value_type><br>**make_span**( with_container_t, Container & cont ) |
-| &nbsp; | < C++11  | template&lt;class Container><br>span&lt;const typename Container::value_type><br>**make_span**( with_container_t, Container const & cont ) |
+| &nbsp; | &nbsp;   | template&lt;class Container><br>span&lt;typename Container::value_type><br>**make_span**( with_container_t, Container & cont ) |
+| &nbsp; | &nbsp;   | template&lt;class Container><br>span&lt;const typename Container::value_type><br>**make_span**( with_container_t, Container const & cont ) |
 | &nbsp; | < C++11  | template&lt;class T, Allocator><br>span&lt;T><br>**make_span**(std::vector&lt;T, Allocator> & cont) |
 | &nbsp; | < C++11  | template&lt;class T, Allocator><br>span&lt;const T><br>**make_span**(std::vector&lt;T, Allocator> const & cont) |
+| &nbsp; | &nbsp;   | &nbsp; |                                       
+| **Free functions**|&nbsp;| macro **`span_CONFIG_PROVIDE_BYTE_SPAN`** |
+| &nbsp; | &nbsp;   | template&lt;class T><br>span&lt;T, sizeof(T)><br>**byte_span**(T & t) |
+| &nbsp; | &nbsp;   | template&lt;class T><br>span&lt;const T, sizeof(T)><br>**byte_span**(T const & t) |
 
 
 Configuration
@@ -130,6 +139,10 @@ Define this to 1 to select *span lite*'s `nonstd::span`. Default is undefined.
 -D<b>span_CONFIG_PROVIDE_MAKE_SPAN</b>=1  
 Define this to 1 to provide creator functions `nonstd::make_span`. Default is undefined.
 
+### Provide `byte_span` functions
+-D<b>span_CONFIG_PROVIDE_BYTE_SPAN</b>=1  
+Define this to 1 to provide creator functions `nonstd::byte_span`. Default is undefined.
+
 ### Contract violation response macros
 
 *span-lite* provides contract violation response control as suggested in proposal [N4415](http://wg21.link/n4415).

include/nonstd/span.hpp

@@ -935,6 +935,8 @@ as_writeable_bytes( span<T,Extent> spn ) span_noexcept
 }  // namespace span_lite
 }  // namespace nonstd
 
+// make available in nonstd:
+
 namespace nonstd {
 
 using span_lite::dynamic_extent;
@@ -1056,10 +1058,42 @@ make_span( with_container_t, Container const & cont ) span_noexcept
 }  // namespace span_lite
 }  // namespace nonstd
 
+// make available in nonstd:
+
 namespace nonstd {
 using span_lite::make_span;
 }  // namespace nonstd
 
 #endif // span_CONFIG_PROVIDE_MAKE_SPAN
 
+#if span_CONFIG_PROVIDE_BYTE_SPAN && span_HAVE( BYTE )
+
+namespace nonstd {
+namespace span_lite {
+
+template< class T >
+inline span_constexpr auto
+byte_span( T & t ) span_noexcept -> span< std::byte, sizeof(t) >
+{
+    return span< std::byte, sizeof(t) >( reinterpret_cast< std::byte * >( &t ), sizeof(t) );
+}
+
+template< class T >
+inline span_constexpr auto
+byte_span( T const & t ) span_noexcept -> span< const std::byte, sizeof(t) >
+{
+    return span< const std::byte, sizeof(t) >( reinterpret_cast< std::byte const * >( &t ), sizeof(t) );
+}
+
+}  // namespace span_lite
+}  // namespace nonstd
+
+// make available in nonstd:
+
+namespace nonstd {
+using span_lite::byte_span;
+}  // namespace nonstd
+
+#endif // span_CONFIG_PROVIDE_BYTE_SPAN
+
 #endif  // NONSTD_SPAN_HPP_INCLUDED

test/CMakeLists.txt

@@ -20,7 +20,8 @@ set( HDRPATH ${HDRDIR}/${HDRNAME} )
 set( OPTIONS "" )
 set( SPAN_CONFIG
     -Dspan_CONFIG_CONTRACT_VIOLATION_THROWS
-    -Dspan_CONFIG_PROVIDE_MAKE_SPAN=1 )
+    -Dspan_CONFIG_PROVIDE_MAKE_SPAN=1
+    -Dspan_CONFIG_PROVIDE_BYTE_SPAN=1 )
 
 set( HAS_STD_FLAGS  FALSE )
 set( HAS_CPP98_FLAG FALSE )

test/span.t.cpp

@@ -1050,6 +1050,38 @@ CASE( "make_span(): Allows building from a const container (with_container_t, st
 
 #endif // span_CONFIG_PROVIDE_MAKE_SPAN
 
+#if span_CONFIG_PROVIDE_BYTE_SPAN
+
+CASE( "byte_span(): Allows building a span of std::byte from a single object (C++17)" )
+{
+# if span_HAVE( BYTE )
+    int x = std::numeric_limits<int>::max();
+
+    span<std::byte> spn = byte_span( x );
+
+    EXPECT( spn.size() == std::ptrdiff_t( sizeof x ) );
+    EXPECT( spn[0]     == std::byte( 0xff ) );
+#else
+    EXPECT( !!"std::byte is not available (no C++17)" );
+#endif
+}
+
+CASE( "byte_span(): Allows building a span of const std::byte from a single const object (C++17)" )
+{
+# if span_HAVE( BYTE )
+    const int x = std::numeric_limits<int>::max();
+
+    span<const std::byte> spn = byte_span( x );
+
+    EXPECT( spn.size() == std::ptrdiff_t( sizeof x ) );
+    EXPECT( spn[0]     == std::byte( 0xff ) );
+#else
+    EXPECT( !!"std::byte is not available (no C++17)" );
+#endif
+}
+
+#endif // span_CONFIG_PROVIDE_BYTE_SPAN
+
 // Issues
 
 #include <cassert>

test/t.bat

@@ -5,7 +5,8 @@ if not "%std%"=="" set std=-std:%std%
 ::set    stdspn=-Dspan_CONFIG_SELECT_STD_SPAN=1 -Dspan_CONFIG_SELECT_NONSTD_SPAN=1 
 set  contract=-Dspan_CONFIG_CONTRACT_VIOLATION_TERMINATES=0 -Dspan_CONFIG_CONTRACT_VIOLATION_THROWS=1
 set make_span=-Dspan_CONFIG_PROVIDE_MAKE_SPAN=1
+set byte_span=-Dspan_CONFIG_PROVIDE_BYTE_SPAN=1
 
-cl -W3 -EHsc %std% %stdspn% %contract% %make_span% -I../include/nonstd span-main.t.cpp span.t.cpp && span-main.t.exe
+cl -W3 -EHsc %std% %stdspn% %contract% %make_span% %byte_span% -DNOMINMAX -I../include/nonstd span-main.t.cpp span.t.cpp && span-main.t.exe
 endlocal
 

test/tc.bat

@@ -5,9 +5,10 @@ if "%std%"=="" set std=c++14
 ::set    stdspn=-Dspan_CONFIG_SELECT_STD_SPAN=1 -Dspan_CONFIG_SELECT_NONSTD_SPAN=1 
 set  contract=-Dspan_CONFIG_CONTRACT_VIOLATION_TERMINATES=0 -Dspan_CONFIG_CONTRACT_VIOLATION_THROWS=1
 set make_span=-Dspan_CONFIG_PROVIDE_MAKE_SPAN=1
+set byte_span=-Dspan_CONFIG_PROVIDE_BYTE_SPAN=1
 
 set     clang=C:\Program Files\LLVM\bin\clang
 set     flags=-Wpedantic -Weverything -Wno-c++98-compat -Wno-c++98-compat-pedantic -Wno-padded -Wno-missing-noreturn -Wno-documentation-unknown-command -Wno-documentation-deprecated-sync -Wno-documentation -Wno-weak-vtables -Wno-missing-prototypes -Wno-missing-variable-declarations -Wno-exit-time-destructors -Wno-global-constructors
 
-"%clang%" -std=%std% -O2 -Wall -Wextra %flags% %stdspn% %contract% %make_span% -fms-compatibility-version=19.00 -isystem "%VCInstallDir%include" -isystem "%WindowsSdkDir_71A%include" -I../include/nonstd -o span-main.t.exe span-main.t.cpp span.t.cpp && span-main.t.exe
+"%clang%" -std=%std% -O2 -Wall -Wextra %flags% %stdspn% %contract% %make_span% %byte_span% -fms-compatibility-version=19.00 -isystem "%VCInstallDir%include" -isystem "%WindowsSdkDir_71A%include" -I../include/nonstd -o span-main.t.exe span-main.t.cpp span.t.cpp && span-main.t.exe
 endlocal

test/tg.bat

@@ -5,9 +5,10 @@ if "%std%"=="" set std=c++14
 ::set    stdspn=-Dspan_CONFIG_SELECT_STD_SPAN=1 -Dspan_CONFIG_SELECT_NONSTD_SPAN=1 
 set  contract=-Dspan_CONFIG_CONTRACT_VIOLATION_TERMINATES=0 -Dspan_CONFIG_CONTRACT_VIOLATION_THROWS=1
 set make_span=-Dspan_CONFIG_PROVIDE_MAKE_SPAN=1
+set byte_span=-Dspan_CONFIG_PROVIDE_BYTE_SPAN=1
 
 set     flags=-Wpedantic -Wno-padded -Wno-missing-noreturn
 set       gpp=g++
 
-%gpp% -std=%std% -O2 -Wall -Wextra %flags% %stdspn% %contract% %make_span% -o span-main.t.exe -I../include/nonstd span-main.t.cpp span.t.cpp && span-main.t.exe
+%gpp% -std=%std% -O2 -Wall -Wextra %flags% %stdspn% %contract% %make_span% %byte_span% -o span-main.t.exe -I../include/nonstd span-main.t.cpp span.t.cpp && span-main.t.exe
 endlocal