[libcxx-commits] [libcxx] [libc++][string] P3044R2: sub-`string_view` from `string` (PR #147095)

[Hristo Hristov via libcxx-commits]

================
@@ -46,79 +56,101 @@ void test1(std::basic_string_view<CharT> sv, std::size_t n, size_t pos) {
     assert(sv[pos + i] == sv1[i]);
 }
 
-template <typename CharT>
-void test(const CharT* s) {
-  typedef std::basic_string_view<CharT> string_view_t;
+template <typename CharT, typename Test<CharT>::Sub TestSub>
+void testCases(const CharT* s) {
+  std::basic_string_view<CharT> sv(s);
 
-  string_view_t sv1(s);
+  testDetail<CharT, TestSub>(sv, 0, 0);
+  testDetail<CharT, TestSub>(sv, 1, 0);
+  testDetail<CharT, TestSub>(sv, 20, 0);
+  testDetail<CharT, TestSub>(sv, sv.size(), 0);
 
-  test1(sv1, 0, 0);
-  test1(sv1, 1, 0);
-  test1(sv1, 20, 0);
-  test1(sv1, sv1.size(), 0);
+  testDetail<CharT, TestSub>(sv, 100, 3);
 
-  test1(sv1, 0, 3);
-  test1(sv1, 2, 3);
-  test1(sv1, 100, 3);
+  testDetail<CharT, TestSub>(sv, 0, std::basic_string_view<CharT>::npos);
+  testDetail<CharT, TestSub>(sv, 2, std::basic_string_view<CharT>::npos);
+  testDetail<CharT, TestSub>(sv, sv.size(), std::basic_string_view<CharT>::npos);
 
-  test1(sv1, 0, string_view_t::npos);
-  test1(sv1, 2, string_view_t::npos);
-  test1(sv1, sv1.size(), string_view_t::npos);
+  testDetail<CharT, TestSub>(sv, sv.size() + 1, 0);
+  testDetail<CharT, TestSub>(sv, sv.size() + 1, 1);
+  testDetail<CharT, TestSub>(sv, sv.size() + 1, std::basic_string_view<CharT>::npos);
+}
 
-  test1(sv1, sv1.size() + 1, 0);
-  test1(sv1, sv1.size() + 1, 1);
-  test1(sv1, sv1.size() + 1, string_view_t::npos);
+template <typename CharT>
+void testSubs(const CharT* s) {
+  testCases<CharT, &std::basic_string_view<CharT>::substr>(s);
+#if TEST_STD_VER >= 26
+  testCases<CharT, &std::basic_string_view<CharT>::subview>(s);
+#endif // TEST_STD_VER >= 26
 }
 
-int main(int, char**) {
-  test("ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
-  test("ABCDE");
-  test("a");
-  test("");
+void test() {
+  testSubs("ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
+  testSubs("ABCDE");
+  testSubs("a");
+  testSubs("");
 
 #ifndef TEST_HAS_NO_WIDE_CHARACTERS
-  test(L"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
-  test(L"ABCDE");
-  test(L"a");
-  test(L"");
+  testSubs(
+      L"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
+  testSubs(L"ABCDE");
+  testSubs(L"a");
+  testSubs(L"");
 #endif
 
 #if TEST_STD_VER >= 11
-  test(u"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
-  test(u"ABCDE");
-  test(u"a");
-  test(u"");
-
-  test(U"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
-  test(U"ABCDE");
-  test(U"a");
-  test(U"");
+  testSubs(
+      u"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
+  testSubs(u"ABCDE");
+  testSubs(u"a");
+  testSubs(u"");
+
+  testSubs(
+      U"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
+  testSubs(U"ABCDE");
+  testSubs(U"a");
+  testSubs(U"");
 #endif
+}
+
+#if TEST_STD_VER >= 14
+template <typename Test<char>::Sub TestSub>
+constexpr void testConstexprDetail() {
----------------
H-G-Hristov wrote:

I think the constexpr test was tacked-on later. The original test isn't trivially convertible to constexpr. I see three options:

1. Use my current implementation as it. I tried to add the new alias without changing the nature of the test substr.pass.cpp.
2. Revert the changes to substr.pass.cpp and create a separate modern test such as subview.pass.cpp for string.
3. Rewirte the existing test to make it work for realtime and compile time cases but then any other tests in string_view have the constexpr tests tacked-on.

What would you prefer to have? I start to think that option 2 might be better, although my initial intention was to show with the test that the two functions are identical.

https://github.com/llvm/llvm-project/pull/147095