Expand std::string_view support to str, bytes, memoryview

include/pybind11/cast.h

@@ -27,23 +27,6 @@
 #include <utility>
 #include <vector>
 
-#if defined(PYBIND11_CPP17)
-# if defined(__has_include)
-# if __has_include(<string_view>)
-# define PYBIND11_HAS_STRING_VIEW
-# endif
-# elif defined(_MSC_VER)
-# define PYBIND11_HAS_STRING_VIEW
-# endif
-#endif
-#ifdef PYBIND11_HAS_STRING_VIEW
-#include <string_view>
-#endif
-
-#if defined(__cpp_lib_char8_t) && __cpp_lib_char8_t >= 201811L
-# define PYBIND11_HAS_U8STRING
-#endif
-
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
 

include/pybind11/detail/common.h

@@ -183,6 +183,21 @@
 # define PYBIND11_HAS_VARIANT 1
 #endif
 
+#if defined(PYBIND11_CPP17)
+# if defined(__has_include)
+# if __has_include(<string_view>)
+# define PYBIND11_HAS_STRING_VIEW
+# endif
+# elif defined(_MSC_VER)
+# define PYBIND11_HAS_STRING_VIEW
+# endif
+#endif
+
+#if defined(__cpp_lib_char8_t) && __cpp_lib_char8_t >= 201811L
+# define PYBIND11_HAS_U8STRING
+#endif
+
+
 #include <Python.h>
 #include <frameobject.h>
 #include <pythread.h>

include/pybind11/pytypes.h

@@ -18,6 +18,10 @@
 # include <optional>
 #endif
 
+#ifdef PYBIND11_HAS_STRING_VIEW
+# include <string_view>
+#endif
+
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 /* A few forward declarations */
@@ -1085,6 +1089,20 @@ class str : public object {
  // NOLINTNEXTLINE(google-explicit-constructor)
  str(const std::string &s) : str(s.data(), s.size()) { }
 
+#ifdef PYBIND11_HAS_STRING_VIEW
+ // enable_if is needed to avoid "ambiguous conversion" errors (see PR #3521).
+ template <typename T, detail::enable_if_t<std::is_same<T, std::string_view>::value, int> = 0>
+ // NOLINTNEXTLINE(google-explicit-constructor)
+ str(T s) : str(s.data(), s.size()) { }
+
+# ifdef PYBIND11_HAS_U8STRING
+ // reinterpret_cast here is safe (C++20 guarantees char8_t has the same size/alignment as char)
+ // NOLINTNEXTLINE(google-explicit-constructor)
+ str(std::u8string_view s) : str(reinterpret_cast<const char*>(s.data()), s.size()) { }
+# endif
+
+#endif
+
  explicit str(const bytes &b);
 
  /** \rst
@@ -1167,6 +1185,26 @@ class bytes : public object {
  pybind11_fail("Unable to extract bytes contents!");
  return std::string(buffer, (size_t) length);
  }
+
+#ifdef PYBIND11_HAS_STRING_VIEW
+ // enable_if is needed to avoid "ambiguous conversion" errors (see PR #3521).
+ template <typename T, detail::enable_if_t<std::is_same<T, std::string_view>::value, int> = 0>
+ // NOLINTNEXTLINE(google-explicit-constructor)
+ bytes(T s) : bytes(s.data(), s.size()) { }
+
+ // Obtain a string view that views the current `bytes` buffer value. Note that this is only
+ // valid so long as the `bytes` instance remains alive and so generally should not outlive the
+ // lifetime of the `bytes` instance.
+ // NOLINTNEXTLINE(google-explicit-constructor)
+ operator std::string_view() const {
+ char *buffer = nullptr;
+ ssize_t length = 0;
+ if (PYBIND11_BYTES_AS_STRING_AND_SIZE(m_ptr, &buffer, &length))
+ pybind11_fail("Unable to extract bytes contents!");
+ return {buffer, static_cast<size_t>(length)};
+ }
+#endif
+
 };
 // Note: breathe >= 4.17.0 will fail to build docs if the below two constructors
 // are included in the doxygen group; close here and reopen after as a workaround
@@ -1714,6 +1752,13 @@ class memoryview : public object {
  static memoryview from_memory(const void *mem, ssize_t size) {
  return memoryview::from_memory(const_cast<void*>(mem), size, true);
  }
+
+#ifdef PYBIND11_HAS_STRING_VIEW
+ static memoryview from_memory(std::string_view mem) {
+ return from_memory(const_cast<char*>(mem.data()), static_cast<ssize_t>(mem.size()), true);
+ }
+#endif
+
 #endif
 };
 

tests/test_builtin_casters.cpp

@@ -140,11 +140,35 @@ TEST_SUBMODULE(builtin_casters, m) {
  m.def("string_view16_return", []() { return std::u16string_view(u"utf16 secret \U0001f382"); });
  m.def("string_view32_return", []() { return std::u32string_view(U"utf32 secret \U0001f382"); });
 
+ // The inner lambdas here are to also test implicit conversion
+ using namespace std::literals;
+ m.def("string_view_bytes", []() { return [](py::bytes b) { return b; }("abc \x80\x80 def"sv); });
+ m.def("string_view_str", []() { return [](py::str s) { return s; }("abc \342\200\275 def"sv); });
+ m.def("string_view_from_bytes", [](const py::bytes &b) { return [](std::string_view s) { return s; }(b); });
+#if PY_MAJOR_VERSION >= 3
+ m.def("string_view_memoryview", []() {
+ static constexpr auto val = "Have some \360\237\216\202"sv;
+ return py::memoryview::from_memory(val);
+ });
+#endif
+
 # ifdef PYBIND11_HAS_U8STRING
  m.def("string_view8_print", [](std::u8string_view s) { py::print(s, s.size()); });
  m.def("string_view8_chars", [](std::u8string_view s) { py::list l; for (auto c : s) l.append((std::uint8_t) c); return l; });
  m.def("string_view8_return", []() { return std::u8string_view(u8"utf8 secret \U0001f382"); });
+ m.def("string_view8_str", []() { return py::str{std::u8string_view{u8"abc ‽ def"}}; });
 # endif
+
+ struct TypeWithBothOperatorStringAndStringView {
+ // NOLINTNEXTLINE(google-explicit-constructor)
+ operator std::string() const { return "success"; }
+ // NOLINTNEXTLINE(google-explicit-constructor)
+ operator std::string_view() const { return "failure"; }
+ };
+ m.def("bytes_from_type_with_both_operator_string_and_string_view",
+ []() { return py::bytes(TypeWithBothOperatorStringAndStringView()); });
+ m.def("str_from_type_with_both_operator_string_and_string_view",
+ []() { return py::str(TypeWithBothOperatorStringAndStringView()); });
 #endif
 
  // test_integer_casting

tests/test_builtin_casters.py

@@ -206,6 +206,17 @@ def test_string_view(capture):
  """
  )
 
+ assert m.string_view_bytes() == b"abc \x80\x80 def"
+ assert m.string_view_str() == u"abc ‽ def"
+ assert m.string_view_from_bytes(u"abc ‽ def".encode("utf-8")) == u"abc ‽ def"
+ if hasattr(m, "has_u8string"):
+ assert m.string_view8_str() == u"abc ‽ def"
+ if not env.PY2:
+ assert m.string_view_memoryview() == "Have some 🎂".encode()
+
+ assert m.bytes_from_type_with_both_operator_string_and_string_view() == b"success"
+ assert m.str_from_type_with_both_operator_string_and_string_view() == "success"
+
 
 def test_integer_casting():
  """Issue #929 - out-of-range integer values shouldn't be accepted"""