Add constexpr support to allocators for C++20 #603
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This adds the `constexpr` attribute on each allocator member function,
including ctors and dtors, to enable easier use of these allocators in
compile-time execution. A practical example of this would be a modern
C++ string class which supports constexpr construction, usage, and
destruction. Without this change, the C++ compiler will not allow
such a class.
An trivial example to show the usage:
```cpp
struct string
{
constexpr string() = default;
constexpr ~string() = default;
gc_allocator<char> a;
};
int main()
{ }
```
This fails to compile before this commit and succeeds afterward. I am
using these changes in practice within jank's [0] compiler and runtime
here [1].
Note that `constexpr` itself was added in C++11, but it can't apply to
destructors until C++20, and it's coming on 2024, so I've skipped over
trying to juggle the different levels of `constexpr` here by just saying
if you have C++20, you can do what we need.
[0]: https://github.com/jank-lang/jank
[1]: https://github.com/jank-lang/jank/pull/50/files#diff-e0a05b8607cd30211eacb4bc222986254ed8af3942ae602092ca3dbd150121d4
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Looks good! |
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Nice, glad to hear it. Thanks for the quick review. Ready when you are. |
ivmai
pushed a commit
that referenced
this pull request
Dec 31, 2023
PR #603 (bdwgc). This adds the `constexpr` attribute on each allocator member function, including ctors and dtors, to enable easier use of these allocators in compile-time execution. A practical example of this would be a modern C++ string class which supports constexpr construction, usage, and destruction. Without this change, the C++ compiler will not allow such a class. * include/gc/gc_allocator.h (gc_allocator, traceable_allocator, gc_allocator_ignore_off_page): Declare all member functions as GC_CONSTEXPR; reformat code. * include/gc/gc_config_macros.h [__cplusplus && !GC_CONSTEXPR] (GC_CONSTEXPR): Define macro.
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Merged. Thank you! |
ivmai
pushed a commit
that referenced
this pull request
Feb 2, 2024
(a cherry-pick of commit 9702965 from 'master') PR #603 (bdwgc). This adds the `constexpr` attribute on each allocator member function, including ctors and dtors, to enable easier use of these allocators in compile-time execution. A practical example of this would be a modern C++ string class which supports constexpr construction, usage, and destruction. Without this change, the C++ compiler will not allow such a class. * include/gc_allocator.h (gc_allocator, traceable_allocator, gc_allocator_ignore_off_page): Declare all member functions as GC_CONSTEXPR; reformat code. * include/gc_config_macros.h [__cplusplus && !GC_CONSTEXPR] (GC_CONSTEXPR): Define macro.
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This adds the
constexprattribute on each allocator member function, including ctors and dtors, to enable easier use of these allocators in compile-time execution. A practical example of this would be a modern C++ string class which supports constexpr construction, usage, and destruction. Without this change, the C++ compiler will not allow such a class.An trivial example to show the usage:
This fails to compile before this commit and succeeds afterward. I am using these changes in practice within jank's 0 compiler and runtime here 1.
Note that
constexpritself was added in C++11, but it can't apply to destructors until C++20, and it's coming on 2024, so I've skipped over trying to juggle the different levels ofconstexprhere by just saying if you have C++20, you can do what we need.