[impl] add interop with std::string_view

biojppm · May 9, 2023 · 7feda45 · 7feda45
1 parent d78a450
commit 7feda45
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Showing 6 changed files with 115 additions and 10 deletions.
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -50,6 +50,7 @@ set(C4CORE_SRC_FILES
     c4/std/std_fwd.hpp
     c4/std/string.hpp
     c4/std/string_fwd.hpp
+    c4/std/string_view.hpp
     c4/std/tuple.hpp
     c4/std/vector.hpp
     c4/std/vector_fwd.hpp

diff --git a/changelog/current.md b/changelog/current.md
@@ -26,6 +26,13 @@ assert(to_substr((char*)ptr).len == 3); // as before
   - add simultaneous ctors from `char[]` and `char*`. Using SFINAE to narrow the `char*` overload prevents it from overriding the `char[]` overload. Thanks to @huangqinjin for the idea (see [#97](https://github.com/biojppm/c4core/issues/97)).
   - remove unneeded constructors of `csubstr` from non-const chars.
   - to each single-argument ctor, add corresponding functions `to_csubstr()` and `to_substr()` to enable clients coercing their types in generic code such as `c4::cat()` and `c4::format()`.
+  - Add interop with `std::string_view` when the standard is at least C++17 ([#PR101](https://github.com/biojppm/c4core/pulls/101)):
+    - provided in the header [`c4/std/string_view.hpp`](src/c4/std/string_view.hpp)
+    - similarly to existing interop headers, this is opt-in and requires explicit inclusion
+    - implemented:
+      - `to_csubstr()` (since `std::string_view` is not writeable, cannot provide `to_csubstr()`)
+      - `to_chars()` (since `std::string_view` is not writeable, cannot provide `from_chars()`)
+      - comparison operators
 - [PR#105](https://github.com/biojppm/c4core/pull/105): Add macros in `c4/language.hpp` for compile-time flow of exceptions:
   - `C4_EXCEPTIONS`: defined when exceptions are enabled
   - `C4_IF_EXCEPTIONS(code_with_exc, code_without_exc)`: select statements for exceptions enabled/disabled
@@ -36,6 +43,7 @@ assert(to_substr((char*)ptr).len == 3); // as before
   - `C4_IF_RTTI_(code_with_rtti, code_without_rtti)`: select code tokens for rtti enabled/disabled
 
 
+
 ### Fixes
 
 - [PR#115](https://github.com/biojppm/c4core/pull/115) - Refactor of `c4::blob`/`c4::cblob`. Use SFINAE to invalidate some of the constructors.

diff --git a/src/c4/std/std.hpp b/src/c4/std/std.hpp
@@ -5,6 +5,7 @@
 
 #include "c4/std/vector.hpp"
 #include "c4/std/string.hpp"
+#include "c4/std/string_view.hpp"
 #include "c4/std/tuple.hpp"
 
 #endif // _C4_STD_STD_HPP_
diff --git a/src/c4/std/string_view.hpp b/src/c4/std/string_view.hpp
@@ -0,0 +1,71 @@
+#ifndef _C4_STD_STRING_VIEW_HPP_
+#define _C4_STD_STRING_VIEW_HPP_
+
+/** @file string_view.hpp */
+
+#ifndef C4CORE_SINGLE_HEADER
+#include "c4/language.hpp"
+#endif
+
+#if (C4_CPP >= 17 && defined(__cpp_lib_string_view))
+
+#ifndef C4CORE_SINGLE_HEADER
+#include "c4/substr.hpp"
+#endif
+
+#include <string_view>
+
+
+namespace c4 {
+
+//-----------------------------------------------------------------------------
+
+/** create a csubstr from an existing std::string_view. */
+C4_ALWAYS_INLINE c4::csubstr to_csubstr(std::string_view s) noexcept
+{
+    return c4::csubstr(s.data(), s.size());
+}
+
+
+//-----------------------------------------------------------------------------
+
+C4_ALWAYS_INLINE bool operator== (c4::csubstr ss, std::string_view s) { return ss.compare(s.data(), s.size()) == 0; }
+C4_ALWAYS_INLINE bool operator!= (c4::csubstr ss, std::string_view s) { return ss.compare(s.data(), s.size()) != 0; }
+C4_ALWAYS_INLINE bool operator>= (c4::csubstr ss, std::string_view s) { return ss.compare(s.data(), s.size()) >= 0; }
+C4_ALWAYS_INLINE bool operator>  (c4::csubstr ss, std::string_view s) { return ss.compare(s.data(), s.size()) >  0; }
+C4_ALWAYS_INLINE bool operator<= (c4::csubstr ss, std::string_view s) { return ss.compare(s.data(), s.size()) <= 0; }
+C4_ALWAYS_INLINE bool operator<  (c4::csubstr ss, std::string_view s) { return ss.compare(s.data(), s.size()) <  0; }
+
+C4_ALWAYS_INLINE bool operator== (std::string_view s, c4::csubstr ss) { return ss.compare(s.data(), s.size()) == 0; }
+C4_ALWAYS_INLINE bool operator!= (std::string_view s, c4::csubstr ss) { return ss.compare(s.data(), s.size()) != 0; }
+C4_ALWAYS_INLINE bool operator<= (std::string_view s, c4::csubstr ss) { return ss.compare(s.data(), s.size()) >= 0; }
+C4_ALWAYS_INLINE bool operator<  (std::string_view s, c4::csubstr ss) { return ss.compare(s.data(), s.size()) >  0; }
+C4_ALWAYS_INLINE bool operator>= (std::string_view s, c4::csubstr ss) { return ss.compare(s.data(), s.size()) <= 0; }
+C4_ALWAYS_INLINE bool operator>  (std::string_view s, c4::csubstr ss) { return ss.compare(s.data(), s.size()) <  0; }
+
+
+//-----------------------------------------------------------------------------
+
+/** copy an std::string_view to a writeable substr */
+inline size_t to_chars(c4::substr buf, std::string_view s)
+{
+    C4_ASSERT(!buf.overlaps(to_csubstr(s)));
+    size_t sz = s.size();
+    size_t len = buf.len < sz ? buf.len : sz;
+    // calling memcpy with null strings is undefined behavior
+    // and will wreak havoc in calling code's branches.
+    // see https://github.com/biojppm/rapidyaml/pull/264#issuecomment-1262133637
+    if(len)
+    {
+        C4_ASSERT(s.data() != nullptr);
+        C4_ASSERT(buf.str != nullptr);
+        memcpy(buf.str, s.data(), len);
+    }
+    return sz; // return the number of needed chars
+}
+
+} // namespace c4
+
+#endif // C4_STRING_VIEW_AVAILABLE
+
+#endif // _C4_STD_STRING_VIEW_HPP_
diff --git a/test/test_std_string.cpp b/test/test_std_string.cpp
@@ -2,6 +2,7 @@
 #ifndef C4CORE_SINGLE_HEADER
 #include "c4/std/string_fwd.hpp"
 #include "c4/std/string.hpp"
+#include "c4/std/string_view.hpp"
 #endif
 
 namespace c4 {
@@ -28,12 +29,26 @@ TEST_CASE("std_string.to_csubstr")
     CHECK_EQ(ss[0], 'B');
 }
 
-TEST_CASE("std_string.compare_csubstr")
+#if (C4_CPP >= 17 && defined(__cpp_lib_string_view))
+TEST_CASE("std_string_view.to_csubstr")
 {
-    std::string s0 = "000";
-    std::string s1 = "111";
-    csubstr ss0 = "000";
-    csubstr ss1 = "111";
+    std::string_view s("barnabe");
+    csubstr ss = to_csubstr(s);
+    CHECK_EQ(ss.str, s.data());
+    CHECK_EQ(ss.len, s.size());
+}
+#endif
+
+#if (C4_CPP >= 17 && defined(__cpp_lib_string_view))
+TEST_CASE_TEMPLATE("std_string.compare_csubstr", T, std::string, std::string_view)
+#else
+TEST_CASE_TEMPLATE("std_string.compare_csubstr", T, std::string)
+#endif
+{
+    T s0 = "000";
+    T s1 = "111";
+    csubstr ss0 = csubstr("0001").first(3);
+    csubstr ss1 = csubstr("1112").first(3);
     CHECK_NE(s0.data(), ss0.data());
     CHECK_NE(s1.data(), ss1.data());
     //
@@ -62,10 +77,14 @@ TEST_CASE("std_string.compare_csubstr")
     CHECK_LT(ss0, s1);
 }
 
-TEST_CASE("std_string.compare_substr")
+#if (C4_CPP >= 17 && defined(__cpp_lib_string_view))
+TEST_CASE_TEMPLATE("std_string.compare_substr", T, std::string, std::string_view)
+#else
+TEST_CASE_TEMPLATE("std_string.compare_substr", T, std::string)
+#endif
 {
-    std::string s0 = "000";
-    std::string s1 = "111";
+    T s0 = "000";
+    T s1 = "111";
     char buf0[] = "000";
     char buf1[] = "111";
     substr ss0 = buf0;
@@ -98,9 +117,13 @@ TEST_CASE("std_string.compare_substr")
     CHECK_LT(ss0, s1);
 }
 
-TEST_CASE("std_string.to_chars")
+#if (C4_CPP >= 17 && defined(__cpp_lib_string_view))
+TEST_CASE_TEMPLATE("std_string.to_chars", T, std::string, std::string_view)
+#else
+TEST_CASE_TEMPLATE("std_string.to_chars", T, std::string)
+#endif
 {
-    const std::string s0 = "000";
+    const T s0 = "000";
     char buf_[100] = {};
     substr buf = buf_;
     CHECK_NE(buf.data(), s0.data());

diff --git a/tools/amalgamate.py b/tools/amalgamate.py
@@ -102,6 +102,7 @@ def amalgamate_c4core(filename: str,
         "src/c4/base64.hpp",
         am.onlyif(with_stl, am.ignfile("src/c4/std/std.hpp")), # this is an umbrella include
         am.onlyif(with_stl, "src/c4/std/string.hpp"),
+        am.onlyif(with_stl, "src/c4/std/string_view.hpp",
         am.onlyif(with_stl, "src/c4/std/vector.hpp"),
         am.onlyif(with_stl, "src/c4/std/tuple.hpp"),
         "src/c4/ext/rng/rng.hpp",