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| 1 | +<?xml version='1.0' encoding='utf-8' standalone='no'?> |
| 2 | +<!DOCTYPE issue SYSTEM "lwg-issue.dtd"> |
| 3 | + |
| 4 | +<issue num="4396" status="New"> |
| 5 | +<title>Improve <code>inplace_vector(from_range_t, R&& rg)</code></title> |
| 6 | +<section><sref ref="[sequence.reqmts]"/><sref ref="[inplace.vector.cons]"/></section> |
| 7 | +<submitter>Hewill Kang</submitter> |
| 8 | +<date>01 Oct 2025</date> |
| 9 | +<priority>99</priority> |
| 10 | + |
| 11 | +<discussion> |
| 12 | +<p> |
| 13 | +Consider: |
| 14 | +</p> |
| 15 | +<blockquote><pre> |
| 16 | +std::array<int, 42> a; |
| 17 | +std::inplace_vector<int, 5> v(std::from_range, a); |
| 18 | +</pre></blockquote> |
| 19 | +<p> |
| 20 | +The above throws `std::bad_alloc` at runtime because the size of `array` is larger than |
| 21 | +capacity of `inplace_vector`. However, we should reject it at compile time since the |
| 22 | +`array` size is a constant expression. |
| 23 | +<p/> |
| 24 | +Given that we do a lot of compile-time size checking in <code><simd></code>, |
| 25 | +it's worth applying that here as well. Compile-time errors are better than runtime ones. |
| 26 | +</p> |
| 27 | +</discussion> |
| 28 | + |
| 29 | +<resolution> |
| 30 | +<p> |
| 31 | +This wording is relative to <paper num="N5014"/>. |
| 32 | +</p> |
| 33 | + |
| 34 | +<ol> |
| 35 | + |
| 36 | +<li><p>Modify <sref ref="[sequence.reqmts]"/> as indicated:</p> |
| 37 | + |
| 38 | +<blockquote> |
| 39 | +<pre> |
| 40 | +a.assign_range(rg) |
| 41 | +</pre> |
| 42 | +<blockquote> |
| 43 | +<p> |
| 44 | +-60- <i>Result</i>: <code>void</code> |
| 45 | +<p/> |
| 46 | +-61- <i>Mandates</i>: <code>assignable_from<T&, ranges::range_reference_t<R>></code> is modeled. |
| 47 | +<ins>For `inplace_vector`, if `ranges::size(rg)` is a constant expression then `ranges::size(rg)` ≤ `a.max_size()`</ins>. |
| 48 | +</p> |
| 49 | +</blockquote> |
| 50 | +</blockquote> |
| 51 | +</li> |
| 52 | + |
| 53 | +<li><p>Modify <sref ref="[inplace.vector.cons]"/> as indicated:</p> |
| 54 | + |
| 55 | +<blockquote> |
| 56 | +<pre> |
| 57 | +template<<i>container-compatible-range</i><T> R> |
| 58 | + constexpr inplace_vector(from_range_t, R&& rg); |
| 59 | +</pre> |
| 60 | +<blockquote> |
| 61 | +<p> |
| 62 | +<ins>-?- <i>Mandates</i>: If `ranges::size(rg)` is a constant expression then `ranges::size(rg)` ≤ `N`.</ins> |
| 63 | +<p/> |
| 64 | +-9- <i>Effects</i>: Constructs an `inplace_vector` with the elements of the range `rg`. |
| 65 | +<p/> |
| 66 | +-10- <i>Complexity</i>: Linear in `ranges::distance(rg)`. |
| 67 | +</p> |
| 68 | +</blockquote> |
| 69 | +</blockquote> |
| 70 | +</li> |
| 71 | +</ol> |
| 72 | + |
| 73 | +</resolution> |
| 74 | + |
| 75 | +</issue> |
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