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doc: document Go 1.17 language changes
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>
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@ -25,12 +25,46 @@ Do not send CLs removing the interior tags from such phrases.
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<h2 id="language">Changes to the language</h2>
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<p><!-- CL 216424 -->
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TODO: <a href="https://golang.org/cl/216424">https://golang.org/cl/216424</a>: allow conversion from slice to array ptr
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<p>
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Go 1.17 includes three small enhancements to the language.
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</p>
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<p><!-- CL 312212 -->
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TODO: <a href="https://golang.org/cl/312212">https://golang.org/cl/312212</a>: add unsafe.Add and unsafe.Slice
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<ul>
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<li><!-- CL 216424; issue 395 -->
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<a href="/ref/spec#Conversions_from_slice_to_array_pointer">Conversions
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from slice to array pointer</a>: An expression <code>s</code> of
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type <code>[]T</code> may now be converted to array pointer type
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<code>*[N]T</code>. If <code>a</code> is the result of such a
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conversion, then corresponding indices that are in range refer to
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the same underlying elements: <code>&a[i] == &s[i]</code>
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for <code>0 <= i < N</code>. The conversion panics if
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<code>len(s)</code> is less than <code>N</code>.
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</li>
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<li><!-- CL 312212; issue 40481 -->
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<a href="/pkg/unsafe#Add"><code>unsafe.Add</code></a>:
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<code>unsafe.Add(ptr, len)</code> adds <code>len</code>
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to <code>ptr</code> and returns the updated pointer
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<code>unsafe.Pointer(uintptr(ptr) + uintptr(len))</code>.
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</li>
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<li><!-- CL 312212; issue 19367 -->
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<a href="/pkg/unsafe#Slice"><code>unsafe.Slice</code></a>:
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For expression <code>ptr</code> of type <code>*T</code>,
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<code>unsafe.Slice(ptr, len)</code> returns a slice of
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type <code>[]T</code> whose underlying array starts
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at <code>ptr</code> and whose length and capacity
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are <code>len</code>.
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</li>
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</ul>
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<p>
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These enhancements were added to simplify writing code that conforms
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to <code>unsafe.Pointer</code>'s <a href="/pkg/unsafe/#Pointer">safety
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rules</a>, but the rules remain unchanged. In particular, existing
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programs that correctly use <code>unsafe.Pointer</code> remain
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valid, and new programs must still follow the rules when
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using <code>unsafe.Add</code> or <code>unsafe.Slice</code>.
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</p>
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<h2 id="ports">Ports</h2>
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