tmp/tmp02amw2i6/{from.md → to.md}
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| 1 |
+
### [[depr]]: compatibility features <a id="diff.cpp23.depr">[[diff.cpp23.depr]]</a>
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**Change:** Remove the type alias `allocator<T>::is_always_equal`.
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**Rationale:** Non-empty allocator classes derived from `allocator`
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needed to explicitly define an `is_always_equal` member type so that
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`allocator_traits` would not use the one from the allocator base class.
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**Effect on original feature:** It is simpler to correctly define an
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| 8 |
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allocator class with an allocator base class.
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[*Example 1*:
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``` cpp
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template <class T>
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struct MyAlloc : allocator<T> {
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int tag;
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};
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static_assert(!allocator_traits<MyAlloc<int>>::is_always_equal); // Error in C++23{},
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// OK in C++26{}
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```
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— *end example*]
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**Change:** Removal of atomic access API for `shared_ptr` objects.
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**Rationale:** The old behavior was brittle. `shared_ptr` objects using
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the old API were not protected by the type system, and certain
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| 27 |
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interactions with code not using this API would, in some cases, silently
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produce undefined behavior. A complete type-safe replacement is provided
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| 29 |
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in the form of `atomic<shared_ptr<T>>`. **Effect on original feature:**
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A valid C++23 program that relies on the presence of the removed
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| 31 |
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functions may fail to compile.
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**Change:** Remove the `basic_string::reserve()` overload with no
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| 34 |
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parameters. **Rationale:** The overload of `reserve` with no parameters
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is redundant. The `shrink_to_fit` member function can be used instead.
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| 36 |
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**Effect on original feature:** A valid C++23 program that calls
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| 37 |
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`reserve()` on a `basic_string` object may fail to compile. The old
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| 38 |
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functionality can be achieved by calling `shrink_to_fit()` instead, or
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| 39 |
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the function call can be safely eliminated with no side effects.
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| 40 |
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**Change:** Remove header `<codecvt>` and all its contents.
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**Rationale:** The header has been deprecated for the previous three
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| 43 |
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editions of this document and no longer implements the current Unicode
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| 44 |
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standard, supporting only the obsolete UCS-2 encoding. Ongoing support
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is at implementer’s discretion, exercising freedoms granted by
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| 46 |
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[[zombie.names]]. **Effect on original feature:** A valid C++23 program
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| 47 |
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`#include`-ing the header or importing the header unit may fail to
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| 48 |
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compile. Code that uses any of the following names by importing the
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| 49 |
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standard library modules may fail to compile:
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| 50 |
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- `codecvt_mode`,
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- `codecvt_utf16`,
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| 53 |
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- `codecvt_utf8`,
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- `codecvt_utf8_utf16`,
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- `consume_header`,
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- `generate_header`, and
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| 57 |
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- `little_endian`.
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| 58 |
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**Change:** Remove header `<strstream>` and all its contents.
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| 60 |
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**Rationale:** The header has been deprecated since the original C++
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| 61 |
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standard; the `<spanstream>` header provides an updated, safer facility.
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| 62 |
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Ongoing support is at implementer’s discretion, exercising freedoms
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| 63 |
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granted by [[zombie.names]]. **Effect on original feature:** A valid
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| 64 |
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C++23 program `#include`-ing the header or importing the header unit may
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| 65 |
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become ill-formed. Code that uses any of the following classes by
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| 66 |
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importing one of the standard library modules may become ill-formed:
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| 67 |
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| 68 |
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- `istrstream`
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| 69 |
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- `ostrstream`
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| 70 |
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- `strstream`
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| 71 |
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- `strstreambuf`
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| 72 |
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| 73 |
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**Change:** Remove convenience interfaces `wstring_convert` and
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| 74 |
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`wbuffer_convert`. **Rationale:** These features were underspecified
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| 75 |
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with no clear error reporting mechanism and were deprecated for the last
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| 76 |
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three editions of this document. Ongoing support is at implementer’s
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| 77 |
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discretion, exercising freedoms granted by [[zombie.names]]. **Effect on
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| 78 |
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original feature:** A valid C++23 program using these interfaces may
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| 79 |
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become ill-formed.
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| 80 |
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