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doc: document Go 1.17 language changes

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Fixes #46020.

Change-Id: Iadf9a0ac4a8863e17155d6ba1af2cc497634a634
Reviewed-on: https://go-review.googlesource.com/c/go/+/325870
Trust: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
This commit is contained in:
Matthew Dempsky 2021-06-07 14:28:14 -07:00
parent dc8b558951
commit 39c39ae52f
1 changed files with 38 additions and 4 deletions
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@ -25,12 +25,46 @@ Do not send CLs removing the interior tags from such phrases.
<h2 id="language">Changes to the language</h2>
<p><!-- CL 216424 -->
TODO: <a href="https://golang.org/cl/216424">https://golang.org/cl/216424</a>: allow conversion from slice to array ptr
<p>
Go 1.17 includes three small enhancements to the language.
</p>
<p><!-- CL 312212 -->
TODO: <a href="https://golang.org/cl/312212">https://golang.org/cl/312212</a>: add unsafe.Add and unsafe.Slice
<ul>
<li><!-- CL 216424; issue 395 -->
<a href="/ref/spec#Conversions_from_slice_to_array_pointer">Conversions
from slice to array pointer</a>: An expression <code>s</code> of
type <code>[]T</code> may now be converted to array pointer type
<code>*[N]T</code>. If <code>a</code> is the result of such a
conversion, then corresponding indices that are in range refer to
the same underlying elements: <code>&amp;a[i] == &amp;s[i]</code>
for <code>0 &lt;= i &lt; N</code>. The conversion panics if
<code>len(s)</code> is less than <code>N</code>.
</li>
<li><!-- CL 312212; issue 40481 -->
<a href="/pkg/unsafe#Add"><code>unsafe.Add</code></a>:
<code>unsafe.Add(ptr, len)</code> adds <code>len</code>
to <code>ptr</code> and returns the updated pointer
<code>unsafe.Pointer(uintptr(ptr) + uintptr(len))</code>.
</li>
<li><!-- CL 312212; issue 19367 -->
<a href="/pkg/unsafe#Slice"><code>unsafe.Slice</code></a>:
For expression <code>ptr</code> of type <code>*T</code>,
<code>unsafe.Slice(ptr, len)</code> returns a slice of
type <code>[]T</code> whose underlying array starts
at <code>ptr</code> and whose length and capacity
are <code>len</code>.
</li>
</ul>
<p>
These enhancements were added to simplify writing code that conforms
to <code>unsafe.Pointer</code>'s <a href="/pkg/unsafe/#Pointer">safety
rules</a>, but the rules remain unchanged. In particular, existing
programs that correctly use <code>unsafe.Pointer</code> remain
valid, and new programs must still follow the rules when
using <code>unsafe.Add</code> or <code>unsafe.Slice</code>.
</p>
<h2 id="ports">Ports</h2>