Implement make_span

doc/core.qbk

@@ -58,6 +58,7 @@ criteria for inclusion is that the utility component be:
 [include is_same.qbk]
 [include launder.qbk]
 [include lightweight_test.qbk]
+[include make_span.qbk]
 [include max_align.qbk]
 [include memory_resource.qbk]
 [include no_exceptions_support.qbk]

doc/make_span.qbk

@@ -0,0 +1,81 @@
+[/
+Copyright 2023 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
+]
+
+[section:make_span make_span]
+
+[simplesect Authors]
+
+* Glen Fernandes
+
+[endsimplesect]
+
+[section Overview]
+
+The header <boost/core/make_span.hpp> provides function templates `make_span`
+to conveniently create `span` objects. They are useful before C++17 where Class
+Template Argument Deduction (CTAD) is not available.
+
+[endsect]
+
+[section Reference]
+
+```
+namespace boost {
+
+template<class I>
+constexpr span<I>
+make_span(I* d, std::size_t n) noexcept;
+
+template<class I>
+constexpr span<I>
+make_span(I* b, I* e) noexcept;
+
+template<class T, std::size_t N>
+constexpr span<T, N>
+make_span(T(&a)[N]) noexcept;
+
+template<class T, std::size_t N>
+constexpr span<T, N>
+make_span(std::array<T, N>& a) noexcept;
+
+template<class T, std::size_t N>
+constexpr span<const T, N>
+make_span(const std::array<T, N>& a) noexcept;
+
+template<class R>
+span<std::remove_pointer_t<decltype(std::declval<R&>().data())> >
+make_span(R&& r);
+
+} /* boost */
+```
+
+[section Functions]
+
+[variablelist
+[[`template<class I> span<I> make_span(I* f, std::size_t c);`]
+[Returns `span<I>(f, c)`.]]
+[[`template<class I> span<I> make_span(I* f, I* l);`]
+[Returns `span<I>(f, l)`.]]
+[[`template<class T, std::size_t N> span<T, N> make_span(T(&a)[N]);`]
+[Returns `span<T, N>(a)`.]]
+[[`template<class T, std::size_t N> span<T, N>
+make_span(std::array<T, N>& a);`]
+[Returns `span<T, N>(a)`.]]
+[[`template<class T, std::size_t N> span<const T, N>
+make_span(const std::array<T, N>& a);`]
+[Returns `span<const T, N>(a)`.]]
+[[`template<class R>
+span<std::remove_pointer_t<decltype(std::declval<R&>().data())> >
+make_span(R&& r);`]
+[Returns `span<>(std::forward<R>(r))`.]]]
+
+[endsect]
+
+[endsect]
+
+[endsect]

include/boost/core/make_span.hpp

@@ -0,0 +1,59 @@
+/*
+Copyright 2023 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
+*/
+#ifndef BOOST_CORE_MAKE_SPAN_HPP
+#define BOOST_CORE_MAKE_SPAN_HPP
+
+#include <boost/core/span.hpp>
+
+namespace boost {
+
+template<class I>
+inline constexpr span<I>
+make_span(I* f, std::size_t c) noexcept
+{
+    return span<I>(f, c);
+}
+
+template<class I>
+inline constexpr span<I>
+make_span(I* f, I* l) noexcept
+{
+    return span<I>(f, l);
+}
+
+template<class T, std::size_t N>
+inline constexpr span<T, N>
+make_span(T(&a)[N]) noexcept
+{
+    return span<T, N>(a);
+}
+
+template<class T, std::size_t N>
+inline constexpr span<T, N>
+make_span(std::array<T, N>& a) noexcept
+{
+    return span<T, N>(a);
+}
+
+template<class T, std::size_t N>
+inline constexpr span<const T, N>
+make_span(const std::array<T, N>& a) noexcept
+{
+    return span<const T, N>(a);
+}
+
+template<class R>
+inline span<typename detail::span_data<R>::type>
+make_span(R&& r)
+{
+    return span<typename detail::span_data<R>::type>(std::forward<R>(r));
+}
+
+} /* boost */
+
+#endif

test/Jamfile.v2

@@ -343,6 +343,7 @@ run span_deduction_guide_test.cpp ;
 run as_bytes_test.cpp ;
 run as_writable_bytes_test.cpp ;
 compile span_boost_begin_test.cpp ;
+run make_span_test.cpp ;
 
 run splitmix64_test.cpp
   : : : $(pedantic-errors) ;

test/make_span_test.cpp

@@ -0,0 +1,100 @@
+/*
+Copyright 2023 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
+*/
+#include <boost/config.hpp>
+#if !defined(BOOST_NO_CXX11_CONSTEXPR) && !defined(BOOST_NO_CXX11_DECLTYPE)
+#include <boost/core/make_span.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+template<class T>
+class range {
+public:
+    T* data() {
+        return &v_[0];
+    }
+
+    std::size_t size() const {
+        return 4;
+    }
+
+private:
+    T v_[4];
+};
+
+void test_data_size()
+{
+    int a[4];
+    boost::span<int> s = boost::make_span(&a[0], 4);
+    BOOST_TEST_EQ(s.data(), &a[0]);
+    BOOST_TEST_EQ(s.size(), 4);
+}
+
+void test_first_last()
+{
+    int a[4];
+    boost::span<int> s = boost::make_span(&a[0], &a[4]);
+    BOOST_TEST_EQ(s.data(), &a[0]);
+    BOOST_TEST_EQ(s.size(), 4);
+}
+
+void test_array()
+{
+    int a[4];
+    boost::span<int, 4> s = boost::make_span(a);
+    BOOST_TEST_EQ(s.data(), &a[0]);
+    BOOST_TEST_EQ(s.size(), 4);
+}
+
+void test_std_array()
+{
+    std::array<int, 4> a;
+    boost::span<int, 4> s = boost::make_span(a);
+    BOOST_TEST_EQ(s.data(), a.data());
+    BOOST_TEST_EQ(s.size(), a.size());
+}
+
+void test_const_std_array()
+{
+    const std::array<int, 4> a = std::array<int, 4>();
+    boost::span<const int> s = boost::make_span(a);
+    BOOST_TEST_EQ(s.data(), a.data());
+    BOOST_TEST_EQ(s.size(), a.size());
+}
+
+void test_range()
+{
+    range<int> c;
+    boost::span<int> s = boost::make_span(c);
+    BOOST_TEST_EQ(s.data(), c.data());
+    BOOST_TEST_EQ(s.size(), c.size());
+}
+
+void test_initializer_list()
+{
+    std::initializer_list<int> l{1, 2};
+    boost::span<const int> s = boost::make_span(l);
+    BOOST_TEST_EQ(s.data(), l.begin());
+    BOOST_TEST_EQ(s.size(), l.size());
+}
+
+int main()
+{
+    test_data_size();
+    test_first_last();
+    test_array();
+    test_std_array();
+    test_const_std_array();
+    test_range();
+    test_initializer_list();
+    return boost::report_errors();
+}
+#else
+int main()
+{
+    return 0;
+}
+#endif