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74 changes: 48 additions & 26 deletions papers/p3235.bs
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Expand Up @@ -15,15 +15,15 @@ Markup Shorthands: markdown yes
Introduction {#intro}
============

P3107 enabled an efficient implementation of `std::print` and applied the
[[P3107]] enabled an efficient implementation of `std::print` and applied the
optimization to fundamental and string types. The current paper applies this
important optimization to other standard types.

Proposal {#proposal}
========

Here is a list of standard formatters that are not yet opted into the
optimization.
`std::print` optimization.

Date and time formatters [[time.syn](https://eel.is/c++draft/time.syn)]:

Expand Down Expand Up @@ -67,32 +67,22 @@ Date and time formatters [[time.syn](https://eel.is/c++draft/time.syn)]:
struct formatter<chrono::zoned_time<Duration, TimeZonePtr>, charT>;
```

`Rep` is an arithmetic type, `Period` is `std::ratio<...>`, `Duration` is
`std::duration<...>` and `charT` is `char` or `wchar_t` so all chrono formatters
except the one for `zoned_time` can be unconditionally opted into the
optimization. The formatter for `zoned_time` can be opted in for the default
`TimeZonePtr` (`const std::chrono::time_zone*`) but not arbitrary user-provided
`TimeZonePtr` that can be potentially locking.

<!-- https://www.godbolt.org/z/v87aY37GG -->

`thread::id` formatter [[thread.thread.id](
https://eel.is/c++draft/thread.thread.id)]:

```
template<class charT> struct formatter<thread::id, charT>;
```

Range formatter [[format.syn](https://eel.is/c++draft/format.syn)]:

```
// [format.range.fmtmap], [format.range.fmtset], [format.range.fmtstr], specializations for maps, sets, and strings
template<ranges::input_range R, class charT>
requires (format_kind<R> != range_format::disabled) &&
formattable<ranges::range_reference_t<R>, charT>
struct formatter<R, charT> : range-default-formatter<format_kind<R>, R, charT> { };
```

Tuple formatter [[format.tuple](https://eel.is/c++draft/format.tuple)]:

```
template<class charT, formattable<charT>... Ts>
struct formatter<pair-or-tuple<Ts...>, charT> {
...
};
```

Stacktrace formatters [[stacktrace.syn](
https://eel.is/c++draft/stacktrace.syn)]:

Expand All @@ -111,6 +101,30 @@ https://eel.is/c++draft/vector.syn)]:
struct formatter<T, charT>;
```

`thread::id`, stacktrace and `vector<bool>` formatters don't invoke any user
code and can be opted into the optimization.

Tuple formatter [[format.tuple](https://eel.is/c++draft/format.tuple)]:

```
template<class charT, formattable<charT>... Ts>
struct formatter<pair-or-tuple<Ts...>, charT> {
...
};
```

The tuple formatter can be opted in if all the element formatters are opted in.

Range formatter [[format.syn](https://eel.is/c++draft/format.syn)]:

```
// [format.range.fmtmap], [format.range.fmtset], [format.range.fmtstr], specializations for maps, sets, and strings
template<ranges::input_range R, class charT>
requires (format_kind<R> != range_format::disabled) &&
formattable<ranges::range_reference_t<R>, charT>
struct formatter<R, charT> : range-default-formatter<format_kind<R>, R, charT> { };
```

`queue` and `priority_queue` formatters [[queue.syn](
https://eel.is/c++draft/queue.syn)]:

Expand All @@ -126,20 +140,28 @@ https://eel.is/c++draft/queue.syn)]:
struct formatter<priority_queue<T, Container, Compare>, charT>;
```

`stack` formatter [[stack.syn](
https://eel.is/c++draft/stack.syn)]:
`stack` formatter [[stack.syn](https://eel.is/c++draft/stack.syn)]:

```
// [container.adaptors.format], formatter specialization for stack
template<class charT, class T, formattable<charT> Container>
struct formatter<stack<T, Container>, charT>;
```

TODO: look into ranges (locking iterator) and custom Container, Compare.

TODO: path

TODO: motivation?

TODO: most are safe except potentially range (locking iterator) and custom
chrono Duration/Rep/Period

TODO: mention that this is a follow-up requested in LEWG discussion

<pre class=biblio>
{
"P3107": {
"title": "Permit an efficient implementation of std::print",
"authors": ["Victor Zverovich"],
"href": "https://wg21.link/p3107"
}
}
</pre>
55 changes: 35 additions & 20 deletions papers/p3235.html
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Expand Up @@ -1563,7 +1563,7 @@
</style>
<meta content="Bikeshed version 4416b18d5, updated Tue Jan 2 15:52:39 2024 -0800" name="generator">
<link href="https://isocpp.org/favicon.ico" rel="icon">
<meta content="e26177053414ef70a3598571b3fb804f77deca67" name="revision">
<meta content="85750f69deb77337f897794d5a3f86d5cad93fa1" name="revision">
<style>/* Boilerplate: style-autolinks */
.css.css, .property.property, .descriptor.descriptor {
color: var(--a-normal-text);
Expand Down Expand Up @@ -2106,16 +2106,20 @@ <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
<ol class="toc" role="directory">
<li><a href="#intro"><span class="secno">1</span> <span class="content">Introduction</span></a>
<li><a href="#proposal"><span class="secno">2</span> <span class="content">Proposal</span></a>
<li>
<a href="#references"><span class="secno"></span> <span class="content">References</span></a>
<ol class="toc">
<li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
</ol>
</ol>
</nav>
<main>
<h2 class="heading settled" data-level="1" id="intro"><span class="secno">1. </span><span class="content">Introduction</span><a class="self-link" href="#intro"></a></h2>
<p>P3107 enabled an efficient implementation of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>print</c-></code> and applied the
<p><a data-link-type="biblio" href="#biblio-p3107" title="Permit an efficient implementation of std::print">[P3107]</a> enabled an efficient implementation of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>print</c-></code> and applied the
optimization to fundamental and string types. The current paper applies this
important optimization to other standard types.</p>
<h2 class="heading settled" data-level="2" id="proposal"><span class="secno">2. </span><span class="content">Proposal</span><a class="self-link" href="#proposal"></a></h2>
<p>Here is a list of standard formatters that are not yet opted into the
optimization.</p>
<p>Here is a list of standard formatters that are not yet opted into the <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>print</c-></code> optimization.</p>
<p>Date and time formatters <a href="https://eel.is/c++draft/time.syn">[time.syn</a>]:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>Rep</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Period</c-><c- p>,</c-> <c- k>class</c-> <c- nc>charT</c-><c- o>></c->
<c- k>struct</c-> <c- nc>formatter</c-><c- o>&lt;</c-><c- n>chrono</c-><c- o>::</c-><c- n>duration</c-><c- o>&lt;</c-><c- n>Rep</c-><c- p>,</c-> <c- n>Period</c-><c- o>></c-><c- p>,</c-> <c- n>charT</c-><c- o>></c-><c- p>;</c->
Expand Down Expand Up @@ -2155,21 +2159,11 @@ <h2 class="heading settled" data-level="2" id="proposal"><span class="secno">2.
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>Duration</c-><c- p>,</c-> <c- k>class</c-> <c- nc>TimeZonePtr</c-><c- p>,</c-> <c- k>class</c-> <c- nc>charT</c-><c- o>></c->
<c- k>struct</c-> <c- nc>formatter</c-><c- o>&lt;</c-><c- n>chrono</c-><c- o>::</c-><c- n>zoned_time</c-><c- o>&lt;</c-><c- n>Duration</c-><c- p>,</c-> <c- n>TimeZonePtr</c-><c- o>></c-><c- p>,</c-> <c- n>charT</c-><c- o>></c-><c- p>;</c->
</pre>
<p><code class="highlight"><c- n>Rep</c-></code> is an arithmetic type, <code class="highlight"><c- n>Period</c-></code> is <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ratio</c-><c- o>&lt;</c-><c- p>...</c-><c- o>></c-></code>, <code class="highlight"><c- n>Duration</c-></code> is <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>duration</c-><c- o>&lt;</c-><c- p>...</c-><c- o>></c-></code> and <code class="highlight"><c- n>charT</c-></code> is <code class="highlight"><c- b>char</c-></code> or <code class="highlight"><c- b>wchar_t</c-></code> so all chrono formatters
except the one for <code class="highlight"><c- n>zoned_time</c-></code> can be unconditionally opted into the
optimization. The formatter for <code class="highlight"><c- n>zoned_time</c-></code> can be opted in for the default <code class="highlight"><c- n>TimeZonePtr</c-></code> (<code class="highlight"><c- k>const</c-> <c- n>std</c-><c- o>::</c-><c- n>chrono</c-><c- o>::</c-><c- n>time_zone</c-><c- o>*</c-></code>) but not arbitrary user-provided <code class="highlight"><c- n>TimeZonePtr</c-></code> that can be potentially locking.</p>
<p><code class="highlight"><c- kr>thread</c-><c- o>::</c-><c- n>id</c-></code> formatter <a href="https://eel.is/c++draft/thread.thread.id">[thread.thread.id</a>]:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>charT</c-><c- o>></c-> <c- k>struct</c-> <c- nc>formatter</c-><c- o>&lt;</c-><c- kr>thread</c-><c- o>::</c-><c- n>id</c-><c- p>,</c-> <c- n>charT</c-><c- o>></c-><c- p>;</c->
</pre>
<p>Range formatter <a href="https://eel.is/c++draft/format.syn">[format.syn</a>]:</p>
<pre class="highlight"><c- c1>// [format.range.fmtmap], [format.range.fmtset], [format.range.fmtstr], specializations for maps, sets, and strings</c->
<c- k>template</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>charT</c-><c- o>></c->
<c- k>requires</c-> <c- p>(</c-><c- n>format_kind</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-> <c- o>!=</c-> <c- n>range_format</c-><c- o>::</c-><c- n>disabled</c-><c- p>)</c-> <c- o>&amp;&amp;</c->
<c- n>formattable</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>charT</c-><c- o>></c->
<c- k>struct</c-> <c- nc>formatter</c-><c- o>&lt;</c-><c- n>R</c-><c- p>,</c-> <c- n>charT</c-><c- o>></c-> <c- o>:</c-> <c- n>range</c-><c- o>-</c-><c- k>default</c-><c- o>-</c-><c- n>formatter</c-><c- o>&lt;</c-><c- n>format_kind</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>R</c-><c- p>,</c-> <c- n>charT</c-><c- o>></c-> <c- p>{</c-> <c- p>};</c->
</pre>
<p>Tuple formatter <a href="https://eel.is/c++draft/format.tuple">[format.tuple</a>]:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>charT</c-><c- p>,</c-> <c- n>formattable</c-><c- o>&lt;</c-><c- n>charT</c-><c- o>></c-><c- p>...</c-> <c- n>Ts</c-><c- o>></c->
<c- k>struct</c-> <c- nc>formatter</c-><c- o>&lt;</c-><c- n>pair</c-><c- o>-</c-><c- k>or</c-><c- o>-</c-><c- n>tuple</c-><c- o>&lt;</c-><c- n>Ts</c-><c- p>...</c-><c- o>></c-><c- p>,</c-> <c- n>charT</c-><c- o>></c-> <c- p>{</c->
<c- p>...</c->
<c- p>};</c->
</pre>
<p>Stacktrace formatters <a href="https://eel.is/c++draft/stacktrace.syn">[stacktrace.syn</a>]:</p>
<pre class="highlight"><c- c1>// [stacktrace.format], formatting support</c->
Expand All @@ -2180,6 +2174,22 @@ <h2 class="heading settled" data-level="2" id="proposal"><span class="secno">2.
<pre class="highlight"><c- c1>// [vector.bool.fmt], formatter specialization for vector&lt;bool></c->
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- k>class</c-> <c- nc>charT</c-><c- o>></c-> <c- k>requires</c-> <c- n>is</c-><c- o>-</c-><c- n>vector</c-><c- o>-</c-><c- b>bool</c-><c- o>-</c-><c- n>reference</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c->
<c- k>struct</c-> <c- nc>formatter</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>charT</c-><c- o>></c-><c- p>;</c->
</pre>
<p><code class="highlight"><c- kr>thread</c-><c- o>::</c-><c- n>id</c-></code>, stacktrace and <code class="highlight"><c- n>vector</c-><c- o>&lt;</c-><c- b>bool</c-><c- o>></c-></code> formatters don’t invoke any user
code and can be opted into the optimization.</p>
<p>Tuple formatter <a href="https://eel.is/c++draft/format.tuple">[format.tuple</a>]:</p>
<pre class="highlight"><c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>charT</c-><c- p>,</c-> <c- n>formattable</c-><c- o>&lt;</c-><c- n>charT</c-><c- o>></c-><c- p>...</c-> <c- n>Ts</c-><c- o>></c->
<c- k>struct</c-> <c- nc>formatter</c-><c- o>&lt;</c-><c- n>pair</c-><c- o>-</c-><c- k>or</c-><c- o>-</c-><c- n>tuple</c-><c- o>&lt;</c-><c- n>Ts</c-><c- p>...</c-><c- o>></c-><c- p>,</c-> <c- n>charT</c-><c- o>></c-> <c- p>{</c->
<c- p>...</c->
<c- p>};</c->
</pre>
<p>The tuple formatter can be opted in if all the element formatters are opted in.</p>
<p>Range formatter <a href="https://eel.is/c++draft/format.syn">[format.syn</a>]:</p>
<pre class="highlight"><c- c1>// [format.range.fmtmap], [format.range.fmtset], [format.range.fmtstr], specializations for maps, sets, and strings</c->
<c- k>template</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>input_range</c-> <c- n>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>charT</c-><c- o>></c->
<c- k>requires</c-> <c- p>(</c-><c- n>format_kind</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-> <c- o>!=</c-> <c- n>range_format</c-><c- o>::</c-><c- n>disabled</c-><c- p>)</c-> <c- o>&amp;&amp;</c->
<c- n>formattable</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>range_reference_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>charT</c-><c- o>></c->
<c- k>struct</c-> <c- nc>formatter</c-><c- o>&lt;</c-><c- n>R</c-><c- p>,</c-> <c- n>charT</c-><c- o>></c-> <c- o>:</c-> <c- n>range</c-><c- o>-</c-><c- k>default</c-><c- o>-</c-><c- n>formatter</c-><c- o>&lt;</c-><c- n>format_kind</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>R</c-><c- p>,</c-> <c- n>charT</c-><c- o>></c-> <c- p>{</c-> <c- p>};</c->
</pre>
<p><code class="highlight"><c- n>queue</c-></code> and <code class="highlight"><c- n>priority_queue</c-></code> formatters <a href="https://eel.is/c++draft/queue.syn">[queue.syn</a>]:</p>
<pre class="highlight"><c- c1>// [container.adaptors.format], formatter specialization for queue</c->
Expand All @@ -2197,10 +2207,9 @@ <h2 class="heading settled" data-level="2" id="proposal"><span class="secno">2.
<c- k>template</c-><c- o>&lt;</c-><c- k>class</c-> <c- nc>charT</c-><c- p>,</c-> <c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <c- n>formattable</c-><c- o>&lt;</c-><c- n>charT</c-><c- o>></c-> <c- n>Container</c-><c- o>></c->
<c- k>struct</c-> <c- nc>formatter</c-><c- o>&lt;</c-><c- n>stack</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Container</c-><c- o>></c-><c- p>,</c-> <c- n>charT</c-><c- o>></c-><c- p>;</c->
</pre>
<p>TODO: look into ranges (locking iterator) and custom Container, Compare.</p>
<p>TODO: path</p>
<p>TODO: motivation?</p>
<p>TODO: most are safe except potentially range (locking iterator) and custom
chrono Duration/Rep/Period</p>
<p>TODO: mention that this is a follow-up requested in LEWG discussion</p>
</main>
<script>
Expand Down Expand Up @@ -2331,4 +2340,10 @@ <h2 class="heading settled" data-level="2" id="proposal"><span class="secno">2.
}

})();
</script>
</script>
<h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
<h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
<dl>
<dt id="biblio-p3107">[P3107]
<dd>Victor Zverovich. <a href="https://wg21.link/p3107"><cite>Permit an efficient implementation of std::print</cite></a>. URL: <a href="https://wg21.link/p3107">https://wg21.link/p3107</a>
</dl>

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