utfview conditional borrowing

bemanproject · Sep 21, 2024 · 43693b8 · 43693b8
1 parent dfc3a01
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diff --git a/include/UtfView/to_utf_view.hpp b/include/UtfView/to_utf_view.hpp
@@ -1162,4 +1162,29 @@ inline constexpr detail::to_utf_impl<char32_t> to_utf32;
 
 /* PAPER: } */
 
+template <class V>
+inline constexpr bool std::ranges::enable_borrowed_range<utfview::to_utf8_view<V>> =
+    std::ranges::enable_borrowed_range<V>;
+
+template <class V>
+inline constexpr bool std::ranges::enable_borrowed_range<utfview::to_utf16_view<V>> =
+    std::ranges::enable_borrowed_range<V>;
+
+template <class V>
+inline constexpr bool std::ranges::enable_borrowed_range<utfview::to_utf32_view<V>> =
+    std::ranges::enable_borrowed_range<V>;
+
+/* PAPER: namespace std::ranges {                                                                              */
+/* PAPER:                                                                                                      */
+/* PAPER:   template <class V>                                                                                 */
+/* PAPER:   inline constexpr bool enable_borrowed_range<std::uc::to_utf8_view<V>> = enable_borrowed_range<V>;  */
+/* PAPER:                                                                                                      */
+/* PAPER:   template <class V>                                                                                 */
+/* PAPER:   inline constexpr bool enable_borrowed_range<std::uc::to_utf16_view<V>> = enable_borrowed_range<V>; */
+/* PAPER:                                                                                                      */
+/* PAPER:   template <class V>                                                                                 */
+/* PAPER:   inline constexpr bool enable_borrowed_range<std::uc::to_utf32_view<V>> = enable_borrowed_range<V>; */
+/* PAPER:                                                                                                      */
+/* PAPER: }                                                                                                    */
+
 #endif // UTFVIEW_TO_UTF_VIEW_HPP
diff --git a/paper/P2728.md b/paper/P2728.md
@@ -278,25 +278,8 @@ In short, rejecting `char` and `wchar_t` forces you to write "`| as_char8_t`"
 everywhere you want to use a `std::string` with the interfaces proposed in
 this paper.
 
-SG-16 has previously expressed support for rejecting `char` and `wchar_t`.
-[Here](https://github.com/sg16-unicode/sg16-meetings/blob/master/README-2023.md#april-12th-2023)
-is the relevant SG-16 poll:
-
-*UTF transcoding interfaces provided by the C++ standard library should
-operate on charN_t types, with support for other types provided by adapters,
-possibly with a special case for char and wchar_t when their associated
-literal encodings are UTF.*
-
-+----+---+---+---+----+
-| SF | F | N | A | SA |
-+====+===+===+===+====+
-| 6  |1  |0  |0  | 1  |
-+----+---+---+---+----+
-
-(This paper ignores the "possibly with a special case for char and
-wchar_t when their associated literal encodings are UTF" part. Making the
-evaluation of a concept change based on the literal encoding seems like a
-flaky move; the literal encoding can change TU to TU.)
+SG-16 has previously expressed strong support for rejecting `char` and
+`wchar_t`, as can be observed in the polling history section.
 
 The feeling in SG-16 was that the `charN_t` types are designed to represent
 UTF encodings, and `char` is not. A `char const *` string could be in any one
@@ -5241,6 +5224,19 @@ namespace std::uc {
 
   inline constexpr @*unspecified*@ to_utf32;
 }
+
+namespace std::ranges {
+
+  template <class V>
+  inline constexpr bool enable_borrowed_range<std::uc::to_utf8_view<V>> = enable_borrowed_range<V>;
+
+  template <class V>
+  inline constexpr bool enable_borrowed_range<std::uc::to_utf16_view<V>> = enable_borrowed_range<V>;
+
+  template <class V>
+  inline constexpr bool enable_borrowed_range<std::uc::to_utf32_view<V>> = enable_borrowed_range<V>;
+
+}
 ```
 
 The exposition-only concept `@*to-utf-view-iterator-optimizable*@` is true if
@@ -5255,7 +5251,7 @@ down.
 The iterator type of `@*to-utf-view-impl*@` is
 `@*utf-iterator*@`. `@*utf-iterator*@` is an iterator that transcodes from
 UTF-N to UTF-M, where N and M are each one of 8, 16, or 32. N may equal
-M. 
+M.
 
 `@*utf-iterator*@` uses a mapping between character types and UTF encodings,
 which is that that `char` and `char8_t` correspond to UTF-8, `char16_t`
@@ -5393,10 +5389,10 @@ expression-equivalent to:
 
 - Otherwise, if `T` is an array type of known bound, then:
 
-  - If the array extent is nonzero and the last element of the array is zero, 
+  - If the array extent is nonzero and the last element of the array is zero,
     then
     `V(std::ranges::subrange(std::ranges::begin(E), --std::ranges::end(E)))`
-  - Otherwise, 
+  - Otherwise,
     `V(std::ranges::subrange(std::ranges::begin(E), std::ranges::end(E)))`
 
 - Otherwise, `V(std::views::all(E))`
@@ -5915,6 +5911,30 @@ exception of `empty_view<T>{} | to_utfN`, the following are always true:
 
 Add the feature test macro `__cpp_lib_unicode_transcoding`.
 
+## Relevant Polls/Minutes
+
+TODO
+
+[Here](https://github.com/sg16-unicode/sg16-meetings/blob/master/README-2023.md#april-12th-2023)
+is the relevant SG-16 poll:
+
+*UTF transcoding interfaces provided by the C++ standard library should
+operate on charN_t types, with support for other types provided by adapters,
+possibly with a special case for char and wchar_t when their associated
+literal encodings are UTF.*
+
++----+---+---+---+----+
+| SF | F | N | A | SA |
++====+===+===+===+====+
+| 6  |1  |0  |0  | 1  |
++----+---+---+---+----+
+
+(This paper ignores the "possibly with a special case for char and
+wchar_t when their associated literal encodings are UTF" part. Making the
+evaluation of a concept change based on the literal encoding seems like a
+flaky move; the literal encoding can change TU to TU.)
+
+
 ## Design notes
 
 None of the proposed interfaces is subject to change in future versions of

diff --git a/src/UtfView/tests/to_utf_view.t.cpp b/src/UtfView/tests/to_utf_view.t.cpp
@@ -1140,6 +1140,10 @@ constexpr bool empty_test() {
   return true;
 }
 
+static_assert(std::ranges::borrowed_range<to_utf8_view<std::string_view>>);
+static_assert(std::ranges::borrowed_range<to_utf16_view<std::string_view>>);
+static_assert(std::ranges::borrowed_range<to_utf32_view<std::string_view>>);
+
 CONSTEXPR_UNLESS_MSVC bool utf_view_test() {
   if (!input_iterator_test(std::initializer_list<char8_t>{u8'x'})) {
     return false;