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spec: change unsafe.Slice((*T)(nil), 0) to return []T(nil)

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Updates #46742.

Change-Id: I044933a657cd1a5cdb29863e49751df5fe9c258a
Reviewed-on: https://go-review.googlesource.com/c/go/+/331069
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Matthew Dempsky 2021-06-25 11:17:43 -07:00
parent 5385e2386b
commit 1519271a93
2 changed files with 12 additions and 3 deletions
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10
doc/go_spec.html
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@ -1,6 +1,6 @@
<!--{ <!--{
"Title": "The Go Programming Language Specification", "Title": "The Go Programming Language Specification",
"Subtitle": "Version of Jun 22, 2021", "Subtitle": "Version of Jun 28, 2021",
"Path": "/ref/spec" "Path": "/ref/spec"
}--> }-->
@ -6789,11 +6789,17 @@ and whose length and capacity are <code>len</code>:
(*[len]ArbitraryType)(unsafe.Pointer(ptr))[:] (*[len]ArbitraryType)(unsafe.Pointer(ptr))[:]
</pre> </pre>
<p>
As a special case, if <code>ptr</code> is <code>nil</code> and <code>len</code> is zero,
<code>Slice</code> returns <code>nil</code>.
</p>
<p> <p>
The <code>len</code> argument must be of integer type or an untyped <a href="#Constants">constant</a>. The <code>len</code> argument must be of integer type or an untyped <a href="#Constants">constant</a>.
A constant <code>len</code> argument must be non-negative and <a href="#Representability">representable</a> by a value of type <code>int</code>; A constant <code>len</code> argument must be non-negative and <a href="#Representability">representable</a> by a value of type <code>int</code>;
if it is an untyped constant it is given type <code>int</code>. if it is an untyped constant it is given type <code>int</code>.
If <code>ptr</code> is <code>nil</code> or <code>len</code> is negative at run time, At run time, if <code>len</code> is negative,
or if <code>ptr</code> is <code>nil</code> and <code>len</code> is not zero,
a <a href="#Run_time_panics">run-time panic</a> occurs. a <a href="#Run_time_panics">run-time panic</a> occurs.
</p> </p>

5
src/unsafe/unsafe.go
View file

@ -221,8 +221,11 @@ func Add(ptr Pointer, len IntegerType) Pointer
// //
// (*[len]ArbitraryType)(unsafe.Pointer(ptr))[:] // (*[len]ArbitraryType)(unsafe.Pointer(ptr))[:]
// //
// As a special case, if ptr is nil and len is zero, Slice returns nil.
//
// The len argument must be of integer type or an untyped constant. // The len argument must be of integer type or an untyped constant.
// A constant len argument must be non-negative and representable by a value of type int; // A constant len argument must be non-negative and representable by a value of type int;
// if it is an untyped constant it is given type int. // if it is an untyped constant it is given type int.
// If ptr is nil or len is negative at run time, a run-time panic occurs. // At run time, if len is negative, or if ptr is nil and len is not zero,
// a run-time panic occurs.
func Slice(ptr *ArbitraryType, len IntegerType) []ArbitraryType func Slice(ptr *ArbitraryType, len IntegerType) []ArbitraryType