[gcc r14-9455] libstdc++: Document that _GLIBCXX_CONCEPT_CHECKS might be removed in future
Jonathan Wakely
redi@gcc.gnu.org
Wed Mar 13 23:51:51 GMT 2024
https://gcc.gnu.org/g:d6490157b3e7ec45a024d1a2acc96e53934dbb0e
commit r14-9455-gd6490157b3e7ec45a024d1a2acc96e53934dbb0e
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Thu Mar 7 12:00:55 2024 +0000
libstdc++: Document that _GLIBCXX_CONCEPT_CHECKS might be removed in future
The macro-based concept checks are unmaintained and do not support C++11
or later, so reject valid code. If nobody plans to update them we should
consider removing them. Alternatively, we could ignore the macro for
C++11 and later, so they have no effect and don't reject valid code.
libstdc++-v3/ChangeLog:
* doc/xml/manual/debug.xml: Document that concept checking might
be removed in future.
* doc/xml/manual/extensions.xml: Likewise.
Diff:
---
libstdc++-v3/doc/xml/manual/debug.xml | 2 ++
libstdc++-v3/doc/xml/manual/extensions.xml | 18 ++++++++++++------
2 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/libstdc++-v3/doc/xml/manual/debug.xml b/libstdc++-v3/doc/xml/manual/debug.xml
index 42d4d32aa29..7f6d0876fc6 100644
--- a/libstdc++-v3/doc/xml/manual/debug.xml
+++ b/libstdc++-v3/doc/xml/manual/debug.xml
@@ -351,6 +351,8 @@
<para> The <link linkend="manual.ext.compile_checks">Compile-Time
Checks</link> extension has compile-time checks for many algorithms.
+ These checks were designed for C++98 and have not been updated to work
+ with C++11 and later standards. They might be removed at a future date.
</para>
</section>
diff --git a/libstdc++-v3/doc/xml/manual/extensions.xml b/libstdc++-v3/doc/xml/manual/extensions.xml
index d4fe2f509d4..490a50cc331 100644
--- a/libstdc++-v3/doc/xml/manual/extensions.xml
+++ b/libstdc++-v3/doc/xml/manual/extensions.xml
@@ -77,8 +77,7 @@ extensions, be aware of two things:
object file. The checks are also cleaner and easier to read and
understand.
</para>
- <para>They are off by default for all versions of GCC from 3.0 to 3.4 (the
- latest release at the time of writing).
+ <para>They are off by default for all GCC 3.0 and all later versions.
They can be enabled at configure time with
<link linkend="manual.intro.setup.configure"><literal>--enable-concept-checks</literal></link>.
You can enable them on a per-translation-unit basis with
@@ -89,10 +88,17 @@ extensions, be aware of two things:
</para>
<para>Please note that the concept checks only validate the requirements
- of the old C++03 standard. C++11 was expected to have first-class
- support for template parameter constraints based on concepts in the core
- language. This would have obviated the need for the library-simulated concept
- checking described above, but was not part of C++11.
+ of the old C++03 standard and reject some valid code that meets the relaxed
+ requirements of C++11 and later standards.
+ C++11 was expected to have first-class support for template parameter
+ constraints based on concepts in the core language.
+ This would have obviated the need for the library-simulated concept checking
+ described above, but was not part of C++11.
+ C++20 adds a different model of concepts, which is now used to constrain
+ some new parts of the C++20 library, e.g. the
+ <filename><ranges></filename> header and the new overloads in the
+ <filename><algorithm></filename> header for working with ranges.
+ The old library-simulated concept checks might be removed at a future date.
</para>
</chapter>
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