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go spec: unsafe.Alignof/Offsetof/Sizeof return uintptr

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This is (indirectly) a language change. Per e-mail discussion
on golang-dev.

Fixes #1943.

R=rsc, iant, r, ken
CC=golang-dev
https://golang.org/cl/4581058
This commit is contained in:
Robert Griesemer 2011-06-13 16:46:42 -07:00
parent 8d8ac637ee
commit eee70b07c1
1 changed files with 15 additions and 12 deletions
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27
doc/go_spec.html
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@ -1,5 +1,5 @@
<!-- title The Go Programming Language Specification --> <!-- title The Go Programming Language Specification -->
<!-- subtitle Version of June 10, 2011 --> <!-- subtitle Version of June 13, 2011 -->
<!-- <!--
TODO TODO
@ -5105,9 +5105,9 @@ package unsafe
type ArbitraryType int // shorthand for an arbitrary Go type; it is not a real type type ArbitraryType int // shorthand for an arbitrary Go type; it is not a real type
type Pointer *ArbitraryType type Pointer *ArbitraryType
func Alignof(variable ArbitraryType) int func Alignof(variable ArbitraryType) uintptr
func Offsetof(selector ArbitraryType) int func Offsetof(selector ArbitraryType) uinptr
func Sizeof(variable ArbitraryType) int func Sizeof(variable ArbitraryType) uintptr
func Reflect(val interface{}) (typ runtime.Type, addr uintptr) func Reflect(val interface{}) (typ runtime.Type, addr uintptr)
func Typeof(val interface{}) (typ interface{}) func Typeof(val interface{}) (typ interface{})
@ -5130,7 +5130,7 @@ For a struct <code>s</code> with field <code>f</code>:
</p> </p>
<pre> <pre>
uintptr(unsafe.Pointer(&amp;s)) + uintptr(unsafe.Offsetof(s.f)) == uintptr(unsafe.Pointer(&amp;s.f)) uintptr(unsafe.Pointer(&amp;s)) + unsafe.Offsetof(s.f) == uintptr(unsafe.Pointer(&amp;s.f))
</pre> </pre>
<p> <p>
@ -5143,12 +5143,12 @@ alignment of the (type of the) variable in bytes. For a variable
</p> </p>
<pre> <pre>
uintptr(unsafe.Pointer(&amp;x)) % uintptr(unsafe.Alignof(x)) == 0 uintptr(unsafe.Pointer(&amp;x)) % unsafe.Alignof(x) == 0
</pre> </pre>
<p> <p>
Calls to <code>Alignof</code>, <code>Offsetof</code>, and Calls to <code>Alignof</code>, <code>Offsetof</code>, and
<code>Sizeof</code> are compile-time constant expressions of type <code>int</code>. <code>Sizeof</code> are compile-time constant expressions of type <code>uintptr</code>.
</p> </p>
<p> <p>
The functions <code>unsafe.Typeof</code>, The functions <code>unsafe.Typeof</code>,
@ -5201,10 +5201,13 @@ The following minimal alignment properties are guaranteed:
</li> </li>
</ol> </ol>
<h2 id="Implementation_differences"><span class="alert">Implementation differences - TODO</span></h2> <span class="alert">
<h2 id="Implementation_differences">Implementation differences - TODO</h2>
<ul> <ul>
<li><span class="alert">The restriction on <code>goto</code> statements and targets (no intervening declarations) is not honored.</span></li> <li>The restriction on <code>goto</code> statements and targets (no intervening declarations) is not honored.</li>
<li><span class="alert"><code>len(a)</code> is only a constant if <code>a</code> is a (qualified) identifier denoting an array or pointer to an array.</span></li> <li><code>len(a)</code> is only a constant if <code>a</code> is a (qualified) identifier denoting an array or pointer to an array.</li>
<li><span class="alert"><code>nil</code> maps are not treated like empty maps.</span></li> <li><code>nil</code> maps are not treated like empty maps.</li>
<li><span class="alert">Trying to send/receive from a <code>nil</code> channel causes a run-time panic.</span></li> <li>Trying to send/receive from a <code>nil</code> channel causes a run-time panic.</li>
<li><code>unsafe.Alignof</code>, <code>unsafe.Offsetof</code>, and <code>unsafe.Sizeof</code> return an <code>int</code>.</li>
</ul> </ul>
</span>