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spec: allow conversion from slice to array ptr

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Implementation follows in subsequent changes.

Updates #395

Change-Id: Ic97ee822805e4c236fdd9d224e776cb2ae62c817
Reviewed-on: https://go-review.googlesource.com/c/go/+/216424
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2020-01-25 11:07:33 -08:00
parent e12b0afa54
commit 1c268431f4
1 changed files with 23 additions and 1 deletions
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24
doc/go_spec.html
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@ -1,6 +1,6 @@
<!--{
"Title": "The Go Programming Language Specification",
"Subtitle": "Version of Mar 16, 2021",
"Subtitle": "Version of Apr 20, 2021",
"Path": "/ref/spec"
}-->
@ -4164,6 +4164,10 @@ in any of these cases:
<li>
<code>x</code> is a string and <code>T</code> is a slice of bytes or runes.
</li>
<li>
<code>x</code> is a slice, <code>T</code> is a pointer to an array,
and the slice and array types have <a href="#Type_identity">identical</a> element types.
</li>
</ul>
<p>
@ -4314,6 +4318,24 @@ MyRunes("白鵬翔") // []rune{0x767d, 0x9d6c, 0x7fd4}
</li>
</ol>
<h4 id="Conversions_from_slice_to_array_pointer">Conversions from slice to array pointer</h4>
<p>
Converting a slice to an array pointer yields a pointer to the underlying array of the slice.
If the <a href="#Length_and_capacity">length</a> of the slice is less than the length of the array,
a <a href="#Run_time_panics">run-time panic<a/> occurs.
</p>
<pre>
s := make([]byte, 2, 4)
s0 := (*[0]byte)(s) // s0 != nil
s2 := (*[2]byte)(s) // &amp;s2[0] == &amp;s[0]
s4 := (*[4]byte)(s) // panics: len([4]byte) > len(s)
var t []string
t0 := (*[0]string)(t) // t0 == nil
t1 := (*[1]string)(t) // panics: len([1]string) > len(s)
</pre>
<h3 id="Constant_expressions">Constant expressions</h3>