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go spec: clarify promotion rules for methods/fields of anonymous fields
Fixes #3635. R=rsc, r, iant, kevlar, iant CC=golang-dev https://golang.org/cl/6217045
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@ -1,6 +1,6 @@
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<!--{
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"Title": "The Go Programming Language Specification",
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"Subtitle": "Version of May 24, 2012",
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"Subtitle": "Version of June 4, 2012",
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"Path": "/ref/spec"
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}-->
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@ -684,6 +684,8 @@ consists of all methods with receiver type <code>T</code>.
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The method set of the corresponding pointer type <code>*T</code>
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is the set of all methods with receiver <code>*T</code> or <code>T</code>
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(that is, it also contains the method set of <code>T</code>).
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Further rules apply to structs containing anonymous fields, as described
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in the section on <a href="#Struct_types">struct types</a>.
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Any other type has an empty method set.
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In a method set, each method must have a
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<a href="#Uniqueness_of_identifiers">unique</a> <a href="#MethodName">method name</a>.
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@ -955,28 +957,39 @@ struct {
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</pre>
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<p>
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Fields and methods (§<a href="#Method_declarations">Method declarations</a>) of an anonymous field are
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promoted to be ordinary fields and methods of the struct (§<a href="#Selectors">Selectors</a>).
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The following rules apply for a struct type <code>S</code> and
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a type named <code>T</code>:
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A field or <a href="#Method_declarations">method</a> <code>f</code> of an
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anonymous field in a struct <code>x</code> is called <i>promoted</i> if
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<code>x.f</code> is a legal <a href="#Selectors">selector</a> that denotes
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that field or method <code>f</code>.
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</p>
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<p>
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Promoted fields act like ordinary fields
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of a struct except that they cannot be used as field names in
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<a href="#Composite_literals">composite literals</a> of the struct.
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</p>
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<p>
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Given a struct type <code>S</code> and a type named <code>T</code>,
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promoted methods are included in the method set of the struct as follows:
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</p>
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<ul>
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<li>If <code>S</code> contains an anonymous field <code>T</code>, the
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<a href="#Method_sets">method set</a> of <code>S</code> includes the
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method set of <code>T</code>.
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<li>
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If <code>S</code> contains an anonymous field <code>T</code>,
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the <a href="#Method_sets">method sets</a> of <code>S</code>
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and <code>*S</code> both include promoted methods with receiver
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<code>T</code>. The method set of <code>*S</code> also
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includes promoted methods with receiver <code>*T</code>.
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</li>
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<li>If <code>S</code> contains an anonymous field <code>*T</code>, the
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method set of <code>S</code> includes the method set of <code>*T</code>
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(which itself includes the method set of <code>T</code>).
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</li>
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<li>If <code>S</code> contains an anonymous field <code>T</code> or
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<code>*T</code>, the method set of <code>*S</code> includes the
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method set of <code>*T</code> (which itself includes the method
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set of <code>T</code>).
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<li>
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If <code>S</code> contains an anonymous field <code>*T</code>,
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the method sets of <code>S</code> and <code>*S</code> both
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include promoted methods with receiver <code>T</code> or
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<code>*T</code>.
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</li>
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</ul>
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<p>
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A field declaration may be followed by an optional string literal <i>tag</i>,
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which becomes an attribute for all the fields in the corresponding
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