improve span container constructor

include/libtorrent/span.hpp

@@ -39,12 +39,35 @@ POSSIBILITY OF SUCH DAMAGE.
 
 namespace libtorrent {
 
+namespace aux {
+
+	template <typename From, typename To>
+	struct compatible_type
+	{
+		// conversions that are OK
+		// int -> int
+		// int const -> int const
+		// int -> int const
+		// int -> int volatile
+		// int -> int const volatile
+		// int volatile -> int const volatile
+		// int const -> int const volatile
+
+		static const bool value = std::is_same<From, To>::value
+			|| std::is_same<From, typename std::remove_const<To>::type>::value
+			|| std::is_same<From, typename std::remove_volatile<To>::type>::value
+			|| std::is_same<From, typename std::remove_cv<To>::type>::value
+			;
+	};
+}
+
 	template <typename T>
 	struct span
 	{
 		span() : m_ptr(nullptr), m_len(0) {}
 
-		template <typename U>
+		template <typename U, typename
+			= typename std::enable_if<aux::compatible_type<U, T>::value>::type>
 		span(span<U> const& v) // NOLINT
 			: m_ptr(v.data()), m_len(v.size()) {}
 
@@ -60,7 +83,10 @@ namespace libtorrent {
 			: m_ptr(&arr[0]), m_len(N) {}
 
 		// anything with a .data() member function is considered a container
-		template <typename Cont, typename = decltype(std::declval<Cont>().data())>
+		// but only if the value type is compatible with T
+		template <typename Cont
+			, typename U = typename std::remove_reference<decltype(*std::declval<Cont>().data())>::type
+			, typename = typename std::enable_if<aux::compatible_type<U, T>::value>::type>
 		span(Cont& c) // NOLINT
 			: m_ptr(c.data()), m_len(c.size()) {}
 
@@ -114,6 +140,14 @@ namespace libtorrent {
 		T* m_ptr;
 		std::size_t m_len;
 	};
+
+	template <class T, class U>
+	inline bool operator==(span<T> const& lhs, span<U> const& rhs)
+	{
+		return  lhs.size()  == rhs.size()
+			&& (lhs.begin() == rhs.begin() || std::equal(lhs.begin(), lhs.end(), rhs.begin()));
+	}
+
 }
 
 #endif // TORRENT_SPAN_HPP_INCLUDED

test/Jamfile

@@ -158,6 +158,7 @@ test-suite libtorrent :
 		]
 
 	[ run test_sha1_hash.cpp ]
+	[ run test_span.cpp ]
 	[ run test_bitfield.cpp ]
 	[ run test_crc32.cpp ]
 	[ run test_ffs.cpp ]

test/Makefile.am

@@ -47,7 +47,8 @@ test_programs = \
   test_linked_list           \
   test_direct_dht            \
   test_ffs                   \
-  test_session_params
+  test_session_params        \
+  test_span
 
 if ENABLE_TESTS
 check_PROGRAMS = $(test_programs)
@@ -241,6 +242,7 @@ test_linked_list_SOURCES = test_linked_list.cpp
 test_direct_dht_SOURCES = test_direct_dht.cpp
 test_ffs_SOURCES = test_ffs.cpp
 test_session_params_SOURCES = test_session_params.cpp
+test_span_SOURCES = test_span.cpp
 
 LDADD = libtest.la $(top_builddir)/src/libtorrent-rasterbar.la
 

test/test_span.cpp

@@ -0,0 +1,112 @@
+/*
+
+Copyright (c) 2017, Arvid Norberg
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in
+      the documentation and/or other materials provided with the distribution.
+    * Neither the name of the author nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+
+*/
+
+#include "libtorrent/config.hpp"
+#include "libtorrent/span.hpp"
+
+#include "test.hpp"
+#include "setup_transfer.hpp"
+
+#include <vector>
+#include <array>
+
+using namespace lt;
+
+span<char const> f(span<char const> x) { return x; }
+span<span<char>> g(span<span<char>> x) { return x; }
+
+TORRENT_TEST(span_vector)
+{
+	std::vector<char> v1 = {1,2,3,4};
+	span<char> a(v1);
+	TEST_CHECK(a == f(v1));
+	TEST_CHECK(a.size() == 4);
+}
+
+TORRENT_TEST(span_std_array)
+{
+	std::array<char, 4> v1{{1,2,3,4}};
+	span<char> a(v1);
+	TEST_CHECK(a == f(v1));
+	TEST_CHECK(a.size() == 4);
+}
+
+TORRENT_TEST(span_const_std_array)
+{
+	std::array<char const, 4> v1{{1,2,3,4}};
+	span<char const> a(v1);
+	TEST_CHECK(a == f(v1));
+	TEST_CHECK(a.size() == 4);
+}
+
+TORRENT_TEST(span_array)
+{
+	char v1[] = {1,2,3,4};
+	span<char> a(v1);
+	TEST_CHECK(a == f(v1));
+	TEST_CHECK(a.size() == 4);
+}
+
+TORRENT_TEST(span_string)
+{
+	std::string v1 = "test";
+	span<char const> a(v1);
+	TEST_CHECK(a == f(v1));
+	TEST_CHECK(a.size() == 4);
+}
+
+TORRENT_TEST(span_const_array)
+{
+	char const v1[] = {1,2,3,4};
+	span<char const> a(v1);
+	TEST_CHECK(a == f(v1));
+	TEST_CHECK(a.size() == 4);
+}
+
+TORRENT_TEST(span_single_element)
+{
+	char const v1 = 1;
+	span<char const> a(v1);
+	TEST_CHECK(a == f(v1));
+	TEST_CHECK(a.size() == 1);
+}
+
+TORRENT_TEST(span_of_spans)
+{
+	std::vector<char> v1 = {1,2,3,4};
+	span<char> s1(v1);
+	span<span<char> > a(s1);
+	TEST_CHECK(a == g(s1));
+	TEST_CHECK(a.size() == 1);
+	TEST_CHECK(a[0].size() == 4);
+}
+