Add an explicit conversion operator from rust::Str to std::string_view.

Author: anforowicz

book/src/binding/str.md

@@ -25,6 +25,9 @@ public:
   Str &operator=(const Str &) & noexcept;
 
   explicit operator std::string() const;
+#if __cplusplus >= 201703L
+  explicit operator std::string_view() const;
+#endif
 
   // Note: no null terminator.
   const char *data() const noexcept;

include/cxx.h

@@ -9,9 +9,6 @@
 #include <iosfwd>
 #include <iterator>
 #include <new>
-#if __cplusplus >= 202002L
-#include <ranges>
-#endif
 #include <stdexcept>
 #include <string>
 #include <type_traits>
@@ -23,6 +20,14 @@
 #include <sys/types.h>
 #endif
 
+#if __cplusplus >= 201703L
+#include <string_view>
+#endif
+
+#if __cplusplus >= 202002L
+#include <ranges>
+#endif
+
 namespace rust {
 inline namespace cxxbridge1 {
 
@@ -123,6 +128,9 @@ class Str final {
   Str &operator=(const Str &) & noexcept = default;
 
   explicit operator std::string() const;
+#if __cplusplus >= 201703L
+  explicit operator std::string_view() const;
+#endif
 
   // Note: no null terminator.
   const char *data() const noexcept;

src/cxx.cc

@@ -325,6 +325,12 @@ Str::operator std::string() const {
   return std::string(this->data(), this->size());
 }
 
+#if __cplusplus >= 201703L
+Str::operator std::string_view() const {
+  return std::string_view(this->data(), this->size());
+}
+#endif
+
 const char *Str::data() const noexcept { return cxxbridge1$str$ptr(this); }
 
 std::size_t Str::size() const noexcept { return cxxbridge1$str$len(this); }

tests/ffi/tests.cc

@@ -874,6 +874,11 @@ extern "C" const char *cxx_run_test() noexcept {
     rust::Str out_param;
     r_return_str_via_out_param(Shared{2020}, out_param);
     ASSERT(out_param == "2020");
+
+#if __cplusplus >= 201703L
+    std::string_view out_param_as_string_view{out_param};
+    ASSERT(out_param_as_string_view == "2020");
+#endif
   }
 
   rust::Str cstr = "test";