P2781R9 std::constant_wrapper #8018
Open
+273
−0
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Fixes 7969 Fixes cplusplus/papers#1458 Allowed paragraphs to number themselves correctly. For consistency, did not use code font for constexpr in the phrase constexpr function. This revision has many Overfull hboxes that will be addressed next commit.
mattkretz
reviewed
Jun 26, 2025
| struct constant_wrapper; | ||
|
|
||
| template<class T> | ||
| concept @\exposid{constexpr-param}@ = requires { typename constant_wrapper<T::value>; }; // \expos |
There was a problem hiding this comment.
Suggested change
| concept @\exposid{constexpr-param}@ = requires { typename constant_wrapper<T::value>; }; // \expos | |
| concept @\defexposconcept{constexpr-param}@ = requires { typename constant_wrapper<T::value>; }; // \expos |
| struct @\exposid{cw-operators}@; // \expos | ||
|
|
||
| template<@\exposid{cw-fixed-value}@ X> | ||
| constexpr auto cw = constant_wrapper<X>{}; |
There was a problem hiding this comment.
Suggested change
| constexpr auto cw = constant_wrapper<X>{}; | |
| constexpr auto @\libglobal{cw} = constant_wrapper<X>{}; |
… I think. I'm still new to indexing, myself. 😉
There was a problem hiding this comment.
There's a missing @ at the end of libglobal{cw}. Otherwise agreed with the approach.
| @@ -624,6 +638,265 @@ | |||
| are used as base classes to define | |||
| the interface for various type traits. | |||
|
|
|||
| \indexlibrarymember{value_type}{integral_constant}% | |||
There was a problem hiding this comment.
This line seems to be a copy&paste left-over?
Comment on lines
+647
to
+649
| using type = T; // \expos | ||
| constexpr @\exposid{cw-fixed-value}@(type v) noexcept: data(v) { } | ||
| T data; // \expos |
There was a problem hiding this comment.
Suggested change
| using type = T; // \expos | |
| constexpr @\exposid{cw-fixed-value}@(type v) noexcept: data(v) { } | |
| T data; // \expos | |
| using @\exposid{type}@ = T; // \expos | |
| constexpr @\exposid{cw-fixed-value}@(type v) noexcept: data(v) { } | |
| T @\exposid{data}@; // \expos |
At least, that's what I recall from review in LWG.
There was a problem hiding this comment.
Both are marked with "// \expos", so should use \exposid decoration, yes. (Also all uses of these identifiers.)
Comment on lines
+654
to
+656
| using type = T[Extent]; // \expos | ||
| constexpr @\exposid{cw-fixed-value}@(T (&arr)[Extent]) noexcept; | ||
| T data[Extent]; // \expos |
| struct @\exposid{cw-operators}@ { // \expos | ||
| // unary operators | ||
| template<@\exposid{constexpr-param}@ T> | ||
| friend constexpr auto operator+(T) noexcept -> constant_wrapper<(+T::value)> |
There was a problem hiding this comment.
Suggested change
| friend constexpr auto operator+(T) noexcept -> constant_wrapper<(+T::value)> | |
| friend constexpr auto @\libmember{operator+}{constant_wrapper}@(T) noexcept -> constant_wrapper<(+T::value)> |
Same for all the other operators. Though, constant_wrapper isn't 100% correct, I believe it's what is most helpful even to implementers.
Comment on lines
+828
to
+830
| struct constant_wrapper: cw-operators { | ||
| static constexpr const auto & value = X.data; | ||
| using type = constant_wrapper; |
There was a problem hiding this comment.
Suggested change
| struct constant_wrapper: cw-operators { | |
| static constexpr const auto & value = X.data; | |
| using type = constant_wrapper; | |
| struct @\libglobal{constant_wrapper}@: cw-operators { | |
| static constexpr const auto & @\libmember{value}{constant_wrapper}@ = X.data; | |
| using @\libmember{type}{constant_wrapper}@ = constant_wrapper; |
etc.
There was a problem hiding this comment.
... and make "data" \exposid, assuming it's the exposition-only thing from earlier.
| \begin{itemdescr} | ||
| \pnum | ||
| \effects | ||
| Initialize elements of \tcode{data} with corresponding elements of \tcode{arr}. |
There was a problem hiding this comment.
Suggested change
| Initialize elements of \tcode{data} with corresponding elements of \tcode{arr}. | |
| Initialize elements of \exposid{data} with corresponding elements of \tcode{arr}. |
mattkretz
reviewed
Jun 26, 2025
|
|
||
| struct @\exposid{cw-operators}@ { // \expos | ||
| // unary operators | ||
| template<@\exposid{constexpr-param}@ T> |
There was a problem hiding this comment.
Suggested change
| template<@\exposid{constexpr-param}@ T> | |
| template<@\exposconcept{constexpr-param}@ T> |
Forgot this one before. Same for all the other uses of constexpr-param
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Fixes #7969
Fixes cplusplus/papers#1458
Allowed paragraphs to number themselves correctly.
For consistency, did not use code font for constexpr in the phrase "constexpr function".