absl::string_view: Add support for starts_with() and ends_with()

when targeting at least C++20

These methods were added to C++20, so they are not available in
earlier language standards. Users requiring compatibility prior to C++20
should use absl::StartsWith() and absl::EndsWith() from
//absl/strings/match.h.

Most users are not affected by this change. By default when targeting at least
C++20 absl::string_view will be an alias for std::string_view. Only users
that have modified //absl/base/options.h will see this change.

PiperOrigin-RevId: 575238435
Change-Id: I7b03fde02c987b30b88c794640c2a616851997d1

1 files changed, 70 insertions, 0 deletions

diff --git a/absl/strings/string_view_test.cc b/absl/strings/string_view_test.cc
index 642989b1..5b1eb01a 100644
--- a/absl/strings/string_view_test.cc
+++ b/absl/strings/string_view_test.cc
@@ -951,6 +951,76 @@ TEST(StringViewTest, At) {
 #endif
 }
 
+#if ABSL_INTERNAL_CPLUSPLUS_LANG >= 202002L
+TEST(StringViewTest, StartsWith) {
+  const absl::string_view a("foobar");
+  const absl::string_view b("123\0abc", 7);
+  const absl::string_view e;
+  EXPECT_TRUE(a.starts_with(a));
+  EXPECT_TRUE(a.starts_with("foo"));
+  EXPECT_TRUE(a.starts_with('f'));
+  EXPECT_TRUE(a.starts_with(e));
+  EXPECT_TRUE(b.starts_with(b));
+  EXPECT_TRUE(b.starts_with('1'));
+  EXPECT_TRUE(b.starts_with(e));
+  EXPECT_TRUE(e.starts_with(""));
+  EXPECT_FALSE(a.starts_with(b));
+  EXPECT_FALSE(b.starts_with(a));
+  EXPECT_FALSE(e.starts_with(a));
+  EXPECT_FALSE(a.starts_with('r'));
+  EXPECT_FALSE(a.starts_with('\0'));
+  EXPECT_FALSE(e.starts_with('r'));
+  EXPECT_FALSE(e.starts_with('\0'));
+
+  // Test that constexpr compiles.
+  constexpr absl::string_view kFooBar("foobar");
+  constexpr absl::string_view kFoo("foo");
+  constexpr absl::string_view kBar("bar");
+  constexpr bool k1 = kFooBar.starts_with(kFoo);
+  EXPECT_TRUE(k1);
+  constexpr bool k2 = kFooBar.starts_with(kBar);
+  EXPECT_FALSE(k2);
+  constexpr bool k3 = kFooBar.starts_with('f');
+  EXPECT_TRUE(k3);
+  constexpr bool k4 = kFooBar.starts_with("fo");
+  EXPECT_TRUE(k4);
+}
+
+TEST(StringViewTest, EndsWith) {
+  const absl::string_view a("foobar");
+  const absl::string_view b("123\0abc", 7);
+  const absl::string_view e;
+  EXPECT_TRUE(a.ends_with(a));
+  EXPECT_TRUE(a.ends_with('r'));
+  EXPECT_TRUE(a.ends_with("bar"));
+  EXPECT_TRUE(a.ends_with(e));
+  EXPECT_TRUE(b.ends_with(b));
+  EXPECT_TRUE(b.ends_with('c'));
+  EXPECT_TRUE(b.ends_with(e));
+  EXPECT_TRUE(e.ends_with(""));
+  EXPECT_FALSE(a.ends_with(b));
+  EXPECT_FALSE(b.ends_with(a));
+  EXPECT_FALSE(e.ends_with(a));
+  EXPECT_FALSE(a.ends_with('f'));
+  EXPECT_FALSE(a.ends_with('\0'));
+  EXPECT_FALSE(e.ends_with('r'));
+  EXPECT_FALSE(e.ends_with('\0'));
+
+  // Test that constexpr compiles.
+  constexpr absl::string_view kFooBar("foobar");
+  constexpr absl::string_view kFoo("foo");
+  constexpr absl::string_view kBar("bar");
+  constexpr bool k1 = kFooBar.ends_with(kFoo);
+  EXPECT_FALSE(k1);
+  constexpr bool k2 = kFooBar.ends_with(kBar);
+  EXPECT_TRUE(k2);
+  constexpr bool k3 = kFooBar.ends_with('r');
+  EXPECT_TRUE(k3);
+  constexpr bool k4 = kFooBar.ends_with("ar");
+  EXPECT_TRUE(k4);
+}
+#endif  // ABSL_INTERNAL_CPLUSPLUS_LANG >= 202002L
+
 struct MyCharAlloc : std::allocator<char> {};
 
 TEST(StringViewTest, ExplicitConversionOperator) {