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go spec: clarification re: method sets of newly declared pointer types

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- added an example to Type declarations section clarifying the
  situation brought up with issue 1324
- slightly re-ordered paragraphs in Types section
- added separate heading for method set section and refer to it
  from elsewhere in the spec
- no language changes

R=rsc, r, iant, ken2, r2
CC=golang-dev
https://golang.org/cl/4145043
This commit is contained in:
Robert Griesemer 2011-02-08 13:31:01 -08:00
parent bf3f768955
commit 2a838d6424
1 changed files with 24 additions and 17 deletions
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41
doc/go_spec.html
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@ -1,5 +1,5 @@
<!-- title The Go Programming Language Specification -->
<!-- subtitle Version of February 4, 2011 -->
<!-- subtitle Version of February 8, 2011 -->
<!--
TODO
@ -609,6 +609,17 @@ interface, slice, map, and channel types&mdash;may be constructed using
type literals.
</p>
<p>
The <i>static type</i> (or just <i>type</i>) of a variable is the
type defined by its declaration. Variables of interface type
also have a distinct <i>dynamic type</i>, which
is the actual type of the value stored in the variable at run-time.
The dynamic type may vary during execution but is always
<a href="#Assignability">assignable</a>
to the static type of the interface variable. For non-interface
types, the dynamic type is always the static type.
</p>
<p>
Each type <code>T</code> has an <i>underlying type</i>: If <code>T</code>
is a predeclared type or a type literal, the corresponding underlying
@ -630,6 +641,7 @@ is <code>string</code>. The underlying type of <code>[]T1</code>, <code>T3</code
and <code>T4</code> is <code>[]T1</code>.
</p>
<h3 id="Method_sets">Method sets</h3>
<p>
A type may have a <i>method set</i> associated with it
(§<a href="#Interface_types">Interface types</a>, §<a href="#Method_declarations">Method declarations</a>).
@ -642,16 +654,6 @@ is the set of all methods with receiver <code>*T</code> or <code>T</code>
Any other type has an empty method set.
In a method set, each method must have a unique name.
</p>
<p>
The <i>static type</i> (or just <i>type</i>) of a variable is the
type defined by its declaration. Variables of interface type
also have a distinct <i>dynamic type</i>, which
is the actual type of the value stored in the variable at run-time.
The dynamic type may vary during execution but is always
<a href="#Assignability">assignable</a>
to the static type of the interface variable. For non-interface
types, the dynamic type is always the static type.
</p>
<h3 id="Boolean_types">Boolean types</h3>
@ -917,7 +919,8 @@ a type named <code>T</code>:
</p>
<ul>
<li>If <code>S</code> contains an anonymous field <code>T</code>, the
method set of <code>S</code> includes the method set of <code>T</code>.
<a href="#Method_sets">method set</a> of <code>S</code> includes the
method set of <code>T</code>.
</li>
<li>If <code>S</code> contains an anonymous field <code>*T</code>, the
@ -1016,7 +1019,7 @@ func(n int) func(p *T)
<h3 id="Interface_types">Interface types</h3>
<p>
An interface type specifies a <a href="#Types">method set</a> called its <i>interface</i>.
An interface type specifies a <a href="#Method_sets">method set</a> called its <i>interface</i>.
A variable of interface type can store a value of any type with a method set
that is any superset of the interface. Such a type is said to
<i>implement the interface</i>.
@ -1678,7 +1681,7 @@ type Cipher interface {
<p>
The declared type does not inherit any <a href="#Method_declarations">methods</a>
bound to the existing type, but the <a href="#Types">method set</a>
bound to the existing type, but the <a href="#Method_sets">method set</a>
of an interface type or of elements of a composite type remains unchanged:
</p>
@ -1691,6 +1694,10 @@ func (m *Mutex) Unlock() { /* Unlock implementation */ }
// NewMutex has the same composition as Mutex but its method set is empty.
type NewMutex Mutex
// The method set of the <a href="#Pointer_types">base type</a> of PtrMutex remains unchanged,
// but the method set of PtrMutex is empty.
type PtrMutex *Mutex
// The method set of *PrintableMutex contains the methods
// Lock and Unlock bound to its anonymous field Mutex.
type PrintableMutex struct {
@ -2594,8 +2601,8 @@ if Join(Split(value, len(value)/2)) != value {
</pre>
<p>
A method call <code>x.m()</code> is valid if the method set of
(the type of) <code>x</code> contains <code>m</code> and the
A method call <code>x.m()</code> is valid if the <a href="#Method_sets">method set</a>
of (the type of) <code>x</code> contains <code>m</code> and the
argument list can be assigned to the parameter list of <code>m</code>.
If <code>x</code> is <a href="#Address_operators">addressable</a> and <code>&amp;x</code>'s method
set contains <code>m</code>, <code>x.m()</code> is shorthand
@ -3058,7 +3065,7 @@ need to be presented regarding send, receive, select, and goroutines.</span>
<h3 id="Method_expressions">Method expressions</h3>
<p>
If <code>M</code> is in the method set of type <code>T</code>,
If <code>M</code> is in the <a href="#Method_sets">method set</a> of type <code>T</code>,
<code>T.M</code> is a function that is callable as a regular function
with the same arguments as <code>M</code> prefixed by an additional
argument that is the receiver of the method.