Some more string_view use, add o3tl::starts/ends_with

...until those C++20 string_view member functions are generally available (the
fallback implementations are taken directly from the C++20 spec).

(In ParseMathMLAttributeLengthValue in starmath/source/mathml/mathmlattr.cxx,
returning nIdx + 2 instead of nIdx + 1 for the single-character u'%' case was
presumably a typo, but which was harmless as the return value was only checked
for <= 0, and has now been turned into a bool.)

Change-Id: Ib441e474c515f016a4d81bb39f7821dfe0356499
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/122322
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 61 insertions, 0 deletions

diff --git a/include/o3tl/string_view.hxx b/include/o3tl/string_view.hxx
index 5ebbb0b9f044..b66ba1175a57 100644
--- a/include/o3tl/string_view.hxx
+++ b/include/o3tl/string_view.hxx
@@ -13,6 +13,7 @@
 
 #include <cassert>
 #include <cstddef>
+#include <string>
 #include <string_view>
 
 #include <rtl/ustring.h>
@@ -46,6 +47,66 @@ inline std::string_view getToken(std::string_view sv, char delimiter, std::size_
     }
     return t;
 }
+
+// Implementations of C++20 std::basic_string_view::starts_with and
+// std::basic_string_view::ends_with, until we can use those directly on all platforms:
+template <typename charT, typename traits = std::char_traits<charT>>
+constexpr bool starts_with(std::basic_string_view<charT, traits> sv,
+                           std::basic_string_view<charT, traits> x) noexcept
+{
+#if defined __cpp_lib_starts_ends_with
+    return sv.starts_with(x);
+#else
+    return sv.substr(0, x.size()) == x;
+#endif
+}
+template <typename charT, typename traits = std::char_traits<charT>>
+constexpr bool starts_with(std::basic_string_view<charT, traits> sv, charT x) noexcept
+{
+#if defined __cpp_lib_starts_ends_with
+    return sv.starts_with(x);
+#else
+    return !sv.empty() && traits::eq(sv.front(), x);
+#endif
+}
+template <typename charT, typename traits = std::char_traits<charT>>
+constexpr bool starts_with(std::basic_string_view<charT, traits> sv, charT const* x)
+{
+#if defined __cpp_lib_starts_ends_with
+    return sv.starts_with(x);
+#else
+    return starts_with(sv, std::basic_string_view<charT, traits>(x));
+#endif
+}
+template <typename charT, typename traits = std::char_traits<charT>>
+constexpr bool ends_with(std::basic_string_view<charT, traits> sv,
+                         std::basic_string_view<charT, traits> x) noexcept
+{
+#if defined __cpp_lib_ends_ends_with
+    return sv.ends_with(x);
+#else
+    return sv.size() >= x.size()
+           && sv.compare(sv.size() - x.size(), std::basic_string_view<charT, traits>::npos, x) == 0;
+#endif
+}
+template <typename charT, typename traits = std::char_traits<charT>>
+constexpr bool ends_with(std::basic_string_view<charT, traits> sv, charT x) noexcept
+{
+#if defined __cpp_lib_ends_ends_with
+    return sv.ends_with(x);
+#else
+    return !sv.empty() && traits::eq(sv.back(), x);
+#endif
+}
+template <typename charT, typename traits = std::char_traits<charT>>
+constexpr bool ends_with(std::basic_string_view<charT, traits> sv, charT const* x)
+{
+#if defined __cpp_lib_ends_ends_with
+    return sv.ends_with(x);
+#else
+    return ends_with(sv, std::basic_string_view<charT, traits>(x));
+#endif
+}
 }
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */