Skip to content

P3016R6 Resolve inconsistencies in begin/end for valarray and braced initializer lists #8544

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 7 commits into
base: main
Choose a base branch
from
Open

P3016R6 Resolve inconsistencies in begin/end for valarray and braced initializer lists #8544

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
7 commits
Select commit Hold shift + click to select a range
3706767
P3016R6 Resolve inconsistencies in begin/end for valarray and braced …
AlisdairM Nov 17, 2025
49a2748
[iterator.range] Turn list of headers into a table
AlisdairM Nov 17, 2025
6e8a21a
Update source/iterators.tex
AlisdairM Nov 22, 2025
c57c177
Update source/iterators.tex
AlisdairM Nov 22, 2025
05d2858
Update source/numerics.tex
AlisdairM Nov 22, 2025
fcda795
[support.initlist.range] Removed section in xrefdelta.tex
AlisdairM Nov 17, 2025
a373bef
[valarray.range] Correct order of arguments to indexlibrarymember
AlisdairM Nov 22, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion source/containers.tex
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -20532,7 +20532,7 @@

\pnum
\effects
Initializes \exposid{data_} with \tcode{il.begin()} and
Initializes \exposid{data_} with \tcode{il.data()} and
\exposid{size_} with \tcode{il.size()}.
\end{itemdescr}

Expand Down
174 changes: 92 additions & 82 deletions source/iterators.tex
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@
\begin{codeblock}
#include <compare> // see \ref{compare.syn}
#include <concepts> // see \ref{concepts.syn}
#include <initializer_list> // see \ref{initializer.list.syn}

namespace std {
template<class T> using @\exposid{with-reference}@ = T&; // \expos
Expand Down Expand Up @@ -464,53 +465,64 @@
class ostreambuf_iterator;

// \ref{iterator.range}, range access
template<class C> constexpr auto begin(C& c) -> decltype(c.begin()); // freestanding
template<class C> constexpr auto begin(const C& c) -> decltype(c.begin()); // freestanding
template<class C> constexpr auto end(C& c) -> decltype(c.end()); // freestanding
template<class C> constexpr auto end(const C& c) -> decltype(c.end()); // freestanding
template<class C> constexpr auto
begin(C& c) noexcept(noexcept(c.begin())) -> decltype(c.begin()); // freestanding
template<class C> constexpr auto
begin(const C& c) noexcept(noexcept(c.begin())) -> decltype(c.begin()); // freestanding
template<class C> constexpr auto
end(C& c) noexcept(noexcept(c.end())) -> decltype(c.end()); // freestanding
template<class C> constexpr auto
end(const C& c) noexcept(noexcept(c.end())) -> decltype(c.end()); // freestanding
Comment on lines +468 to +475
Copy link
Member

@eisenwave eisenwave Nov 17, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

To be honest, I liked the style in the paper better,
which is

  template<class C> constexpr auto begin(C& c)
    noexcept(noexcept(c.begin())) -> decltype(c.begin());

Copy link
Member

@jwakely jwakely Nov 17, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

We usually break after the template-head, and then maybe also break later in the declaration. But I think the <iterator> synopsis is unusual (unique even?) in doing:

template<class C> constexpr auto

Copy link
Member

@jwakely jwakely Nov 17, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

i.e. I think it would be move conventional to do:

template<class C>
  constexpr auto begin(C& c) noexcept(...) -> decltype(...);     // freestanding

and if that doesn't fit, then something like:

template<class C>
  constexpr auto begin(C& c) noexcept(...)
    -> decltype(...);                                            // freestanding

Copy link
Contributor Author

@AlisdairM AlisdairM Nov 22, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I like the more conventional style, but deliberately followed the example of breaking already used throughout this clause. Should I apply our more usual breaking pattern to this header as whole, as a distinct commit?

template<class T, size_t N> constexpr T* begin(T (&array)[N]) noexcept; // freestanding
template<class T, size_t N> constexpr T* end(T (&array)[N]) noexcept; // freestanding
template<class C> constexpr auto cbegin(const C& c) // freestanding
noexcept(noexcept(std::begin(c))) -> decltype(std::begin(c));
template<class C> constexpr auto cend(const C& c) // freestanding
noexcept(noexcept(std::end(c))) -> decltype(std::end(c));
template<class C> constexpr auto rbegin(C& c) -> decltype(c.rbegin()); // freestanding
template<class C> constexpr auto rbegin(const C& c) -> decltype(c.rbegin()); // freestanding
template<class C> constexpr auto rend(C& c) -> decltype(c.rend()); // freestanding
template<class C> constexpr auto rend(const C& c) -> decltype(c.rend()); // freestanding
template<class T, size_t N> constexpr reverse_iterator<T*> rbegin(T (&array)[N]) // freestanding
template<class T, size_t N> constexpr reverse_iterator<T*> rend(T (&array)[N]); // freestanding
template<class C> constexpr auto
cbegin(const C& c) noexcept(noexcept(std::begin(c)))
-> decltype(std::begin(c)); // freestanding
template<class C> constexpr auto
cend(const C& c) noexcept(noexcept(std::end(c))) -> decltype(std::end(c)); // freestanding
template<class C> constexpr auto
rbegin(C& c) noexcept(noexcept(c.rbegin())) -> decltype(c.rbegin()); // freestanding
template<class C> constexpr auto
rbegin(const C& c) noexcept(noexcept(c.rbegin())) -> decltype(c.rbegin()); // freestanding
template<class C> constexpr auto
rend(C& c) noexcept(noexcept(c.rend())) -> decltype(c.rend()); // freestanding
template<class C> constexpr auto
rend(const C& c) noexcept(noexcept(c.rend())) -> decltype(c.rend()); // freestanding
template<class T, size_t N> constexpr reverse_iterator<T*>
rbegin(T (&array)[N]) noexcept; // freestanding
template<class T, size_t N> constexpr reverse_iterator<T*>
rend(T (&array)[N]) noexcept; // freestanding
template<class E> constexpr reverse_iterator<const E*>
rbegin(initializer_list<E> il); // freestanding
rbegin(initializer_list<E> il) noexcept; // freestanding
template<class E> constexpr reverse_iterator<const E*>
rend(initializer_list<E> il); // freestanding
rend(initializer_list<E> il) noexcept; // freestanding
template<class C> constexpr auto
crbegin(const C& c) -> decltype(std::rbegin(c)); // freestanding
crbegin(const C& c) noexcept(noexcept(std::rbegin(c)))
-> decltype(std::rbegin(c)); // freestanding
template<class C> constexpr auto
crend(const C& c) -> decltype(std::rend(c)); // freestanding
crend(const C& c) noexcept(noexcept(std::rend(c))) -> decltype(std::rend(c)); // freestanding

template<class C> constexpr auto
size(const C& c) -> decltype(c.size()); // freestanding
size(const C& c) noexcept(noexcept(c.size())) -> decltype(c.size()); // freestanding
template<class T, size_t N> constexpr size_t
size(const T (&array)[N]) noexcept; // freestanding

template<class C> constexpr auto
ssize(const C& c)
ssize(const C& c) noexcept(noexcept(c.size()))
-> common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>; // freestanding
template<class T, ptrdiff_t N> constexpr ptrdiff_t
ssize(const T (&array)[N]) noexcept; // freestanding

template<class C> constexpr auto
empty(const C& c) -> decltype(c.empty()); // freestanding
empty(const C& c) noexcept(noexcept(c.empty())) -> decltype(c.empty()); // freestanding
template<class T, size_t N> constexpr bool
empty(const T (&array)[N]) noexcept; // freestanding
template<class E> constexpr bool
empty(initializer_list<E> il) noexcept; // freestanding

template<class C> constexpr auto data(C& c) -> decltype(c.data()); // freestanding
template<class C> constexpr auto data(const C& c) -> decltype(c.data()); // freestanding
template<class C> constexpr auto
data(C& c) noexcept(noexcept(c.data())) -> decltype(c.data()); // freestanding
template<class C> constexpr auto
data(const C& c) noexcept(noexcept(c.data())) -> decltype(c.data()); // freestanding
template<class T, size_t N> constexpr T* data(T (&array)[N]) noexcept; // freestanding
template<class E> constexpr const E* data(initializer_list<E> il) noexcept; // freestanding
}
\end{codeblock}

Expand Down Expand Up @@ -7241,28 +7253,38 @@
In addition to being available via inclusion of the \libheader{iterator} header,
the function templates in \ref{iterator.range} are available when any of the following
headers are included:
\libheaderref{array},
\libheaderref{deque},
\libheaderrefx{flat_map}{flat.map.syn},
\libheaderrefx{flat_set}{flat.set.syn},
\libheaderrefx{forward_list}{forward.list.syn},
\libheaderref{hive},
\libheaderrefx{inplace_vector}{inplace.vector.syn},
\libheaderref{list},
\libheaderrefx{map}{associative.map.syn},
\libheaderrefx{regex}{re.syn},
\libheaderrefx{set}{associative.set.syn},
\libheaderref{span},
\libheaderref{string},
\libheaderrefx{string_view}{string.view.synop},
\libheaderrefx{unordered_map}{unord.map.syn},
\libheaderrefx{unordered_set}{unord.set.syn}, and
\libheaderref{vector}.
\begin{multicolfloattable}{Additional range function headers}{range.function.headers}
{lll}
\libheaderref{array} \\
\libheaderref{deque} \\
\libheaderrefx{flat_map}{flat.map.syn} \\
\libheaderrefx{flat_set}{flat.set.syn} \\
\libheaderrefx{forward_list}{forward.list.syn} \\
\libheaderref{hive} \\
\libheaderrefx{inplace_vector}{inplace.vector.syn} \\
\columnbreak
\libheaderref{list} \\
\libheaderrefx{map}{associative.map.syn} \\
\libheaderref{optional} \\
\libheaderrefx{regex}{re.syn} \\
\libheaderrefx{set}{associative.set.syn} \\
\libheaderref{span} \\
\libheaderref{stacktrace} \\
\columnbreak
\libheaderref{string} \\
\libheaderrefx{string_view}{string.view.synop} \\
\libheaderrefx{unordered_map}{unord.map.syn} \\
\libheaderrefx{unordered_set}{unord.set.syn} \\
\libheaderref{valarray} \\
\libheaderref{vector} \\
\end{multicolfloattable}

\indexlibrary{\idxcode{begin(C\&)}}%
\begin{itemdecl}
template<class C> constexpr auto begin(C& c) -> decltype(c.begin());
template<class C> constexpr auto begin(const C& c) -> decltype(c.begin());
template<class C> constexpr auto begin(C& c) noexcept(noexcept(c.begin()))
-> decltype(c.begin());
template<class C> constexpr auto begin(const C& c) noexcept(noexcept(c.begin()))
-> decltype(c.begin());
\end{itemdecl}

\begin{itemdescr}
Expand All @@ -7273,8 +7295,8 @@

\indexlibrary{\idxcode{end(C\&)}}%
\begin{itemdecl}
template<class C> constexpr auto end(C& c) -> decltype(c.end());
template<class C> constexpr auto end(const C& c) -> decltype(c.end());
template<class C> constexpr auto end(C& c) noexcept(noexcept(c.end())) -> decltype(c.end());
template<class C> constexpr auto end(const C& c) noexcept(noexcept(c.end())) -> decltype(c.end());
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -7329,8 +7351,10 @@

\indexlibrary{\idxcode{rbegin(C\&)}}%
\begin{itemdecl}
template<class C> constexpr auto rbegin(C& c) -> decltype(c.rbegin());
template<class C> constexpr auto rbegin(const C& c) -> decltype(c.rbegin());
template<class C> constexpr auto rbegin(C& c) noexcept(noexcept(c.rbegin()))
-> decltype(c.rbegin());
template<class C> constexpr auto rbegin(const C& c) noexcept(noexcept(c.rbegin()))
-> decltype(c.rbegin());
\end{itemdecl}
\begin{itemdescr}
\pnum
Expand All @@ -7340,8 +7364,9 @@

\indexlibrary{\idxcode{rend(C\&)}}%
\begin{itemdecl}
template<class C> constexpr auto rend(C& c) -> decltype(c.rend());
template<class C> constexpr auto rend(const C& c) -> decltype(c.rend());
template<class C> constexpr auto rend(C& c) noexcept(noexcept(c.rend())) -> decltype(c.rend());
template<class C> constexpr auto rend(const C& c) noexcept(noexcept(c.rend()))
-> decltype(c.rend());
\end{itemdecl}
\begin{itemdescr}
\pnum
Expand All @@ -7351,7 +7376,7 @@

\indexlibrary{\idxcode{rbegin(T (\&array)[N])}}%
\begin{itemdecl}
template<class T, size_t N> constexpr reverse_iterator<T*> rbegin(T (&array)[N]);
template<class T, size_t N> constexpr reverse_iterator<T*> rbegin(T (&array)[N]) noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
Expand All @@ -7361,7 +7386,7 @@

\indexlibrary{\idxcode{rend(T (\&array)[N])}}%
\begin{itemdecl}
template<class T, size_t N> constexpr reverse_iterator<T*> rend(T (&array)[N]);
template<class T, size_t N> constexpr reverse_iterator<T*> rend(T (&array)[N]) noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
Expand All @@ -7371,7 +7396,7 @@

\indexlibrary{\idxcode{rbegin(initializer_list<E>)}}%
\begin{itemdecl}
template<class E> constexpr reverse_iterator<const E*> rbegin(initializer_list<E> il);
template<class E> constexpr reverse_iterator<const E*> rbegin(initializer_list<E> il) noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
Expand All @@ -7381,7 +7406,7 @@

\indexlibrary{\idxcode{rend(initializer_list<E>)}}%
\begin{itemdecl}
template<class E> constexpr reverse_iterator<const E*> rend(initializer_list<E> il);
template<class E> constexpr reverse_iterator<const E*> rend(initializer_list<E> il) noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
Expand All @@ -7391,7 +7416,8 @@

\indexlibrary{\idxcode{crbegin(const C\& c)}}%
\begin{itemdecl}
template<class C> constexpr auto crbegin(const C& c) -> decltype(std::rbegin(c));
template<class C> constexpr auto crbegin(const C& c) noexcept(noexcept(std::rbegin(c)))
-> decltype(std::rbegin(c));
\end{itemdecl}
\begin{itemdescr}
\pnum
Expand All @@ -7401,7 +7427,8 @@

\indexlibrary{\idxcode{crend(const C\& c)}}%
\begin{itemdecl}
template<class C> constexpr auto crend(const C& c) -> decltype(std::rend(c));
template<class C> constexpr auto crend(const C& c) noexcept(noexcept(c.crend()))
-> decltype(std::rend(c));
\end{itemdecl}
\begin{itemdescr}
\pnum
Expand All @@ -7411,7 +7438,8 @@

\indexlibrary{\idxcode{size(C\& c)}}%
\begin{itemdecl}
template<class C> constexpr auto size(const C& c) -> decltype(c.size());
template<class C> constexpr auto size(const C& c) noexcept(noexcept(c.size()))
-> decltype(c.size());
\end{itemdecl}
\begin{itemdescr}
\pnum
Expand All @@ -7431,7 +7459,7 @@

\indexlibrary{\idxcode{ssize(C\& c)}}%
\begin{itemdecl}
template<class C> constexpr auto ssize(const C& c)
template<class C> constexpr auto ssize(const C& c) noexcept(noexcept(c.size()))
-> common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>;
\end{itemdecl}
\begin{itemdescr}
Expand All @@ -7455,7 +7483,8 @@

\indexlibrary{\idxcode{empty(C\& c)}}%
\begin{itemdecl}
template<class C> constexpr auto empty(const C& c) -> decltype(c.empty());
template<class C> constexpr auto empty(const C& c) noexcept(noexcept(c.empty()))
-> decltype(c.empty());
\end{itemdecl}
\begin{itemdescr}
\pnum
Expand All @@ -7473,20 +7502,11 @@
\tcode{false}.
\end{itemdescr}

\indexlibrary{\idxcode{empty(initializer_list<E>)}}%
\begin{itemdecl}
template<class E> constexpr bool empty(initializer_list<E> il) noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
\tcode{il.size() == 0}.
\end{itemdescr}

\indexlibrary{\idxcode{data(C\& c)}}%
\begin{itemdecl}
template<class C> constexpr auto data(C& c) -> decltype(c.data());
template<class C> constexpr auto data(const C& c) -> decltype(c.data());
template<class C> constexpr auto data(C& c) noexcept(noexcept(c.data())) -> decltype(c.data());
template<class C> constexpr auto data(const C& c) noexcept(noexcept(c.data()))
-> decltype(c.data());
\end{itemdecl}
\begin{itemdescr}
\pnum
Expand All @@ -7503,13 +7523,3 @@
\returns
\tcode{array}.
\end{itemdescr}

\indexlibrary{\idxcode{data(initializer_list<E>)}}%
\begin{itemdecl}
template<class E> constexpr const E* data(initializer_list<E> il) noexcept;
\end{itemdecl}
\begin{itemdescr}
\pnum
\returns
\tcode{il.begin()}.
\end{itemdescr}
Loading