From 75ad0c1b40d27a2d0749861df923cb38f866a6c2 Mon Sep 17 00:00:00 2001
From: beinhaerter <34543625+beinhaerter@users.noreply.github.com>
Date: Tue, 29 May 2018 04:03:10 +0200
Subject: [PATCH] Add as_bytes for basic_string_span, fixes issue #655 (#683)

---
 include/gsl/string_span     | 15 +++++++++++++++
 tests/string_span_tests.cpp | 19 +++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/include/gsl/string_span b/include/gsl/string_span
index 6b4c839..c08f246 100644
--- a/include/gsl/string_span
+++ b/include/gsl/string_span
@@ -376,6 +376,21 @@ std::basic_string<CharT, Traits, Allocator> to_basic_string(basic_string_span<gC
     return {view.data(), static_cast<std::size_t>(view.length())};
 }
 
+template <class ElementType, std::ptrdiff_t Extent>
+basic_string_span<const byte, details::calculate_byte_size<ElementType, Extent>::value>
+as_bytes(basic_string_span<ElementType, Extent> s) noexcept
+{
+	return { reinterpret_cast<const byte*>(s.data()), s.size_bytes() };
+}
+
+template <class ElementType, std::ptrdiff_t Extent,
+          class = std::enable_if_t<!std::is_const<ElementType>::value>>
+basic_string_span<byte, details::calculate_byte_size<ElementType, Extent>::value>
+as_writeable_bytes(basic_string_span<ElementType, Extent> s) noexcept
+{
+    return {reinterpret_cast<byte*>(s.data()), s.size_bytes()};
+}
+
 // zero-terminated string span, used to convert
 // zero-terminated spans to legacy strings
 template <typename CharT, std::ptrdiff_t Extent = dynamic_extent>
diff --git a/tests/string_span_tests.cpp b/tests/string_span_tests.cpp
index 0032b0f..c0b5b19 100644
--- a/tests/string_span_tests.cpp
+++ b/tests/string_span_tests.cpp
@@ -1167,3 +1167,22 @@ TEST_CASE("char32_t type")
     CHECK(ss8 <= ss9);
     CHECK(ss8 != ss9);
 }
+
+TEST_CASE("as_bytes")
+{
+    cwzstring_span<> v(L"qwerty");
+    const auto s = v.as_string_span();
+    const auto bs = as_bytes(s);
+    CHECK(static_cast<const void*>(bs.data()) == static_cast<const void*>(s.data()));
+    CHECK(bs.size() == s.size_bytes());
+}
+
+TEST_CASE("as_writeable_bytes")
+{
+    wchar_t buf[]{L"qwerty"};
+    wzstring_span<> v(buf);
+    const auto s = v.as_string_span();
+    const auto bs = as_writeable_bytes(s);
+    CHECK(static_cast<const void*>(bs.data()) == static_cast<const void*>(s.data()));
+    CHECK(bs.size() == s.size_bytes());
+}