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spec: clarifications around exports, uniqueness of identifiers

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- Define what it means for two identifiers to be unique.

- The current spec is incorrect about exported
identifiers: for instance, it excluded fields
of non-exported types of exported variables
from being exported. It is easier to leave
the detailed specification away and let the
rest of the spec govern access of exported
identifiers.

- The current spec is incorrect about qualified
identifiers: It simply required that an identifier
be exported to be valid in a qualified identifier.
However, qualified identifiers can only access
exported identifiers declared in the package
block of the imported package.

Fixes #1551.

R=r, rsc, iant, ken
CC=golang-dev
https://golang.org/cl/5711043
This commit is contained in:
Robert Griesemer 2012-03-01 13:57:49 -08:00
parent 3c3c5f38a0
commit 103c9db747
1 changed files with 44 additions and 28 deletions
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72
doc/go_spec.html
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@ -684,7 +684,8 @@ The method set of the corresponding pointer type <code>*T</code>
is the set of all methods with receiver <code>*T</code> or <code>T</code>
(that is, it also contains the method set of <code>T</code>).
Any other type has an empty method set.
In a method set, each method must have a unique <a href="#MethodName">method name</a>.
In a method set, each method must have a
<a href="#Uniqueness_of_identifiers">unique</a> <a href="#MethodName">method name</a>.
</p>
<p>
@ -895,7 +896,7 @@ A struct is a sequence of named elements, called fields, each of which has a
name and a type. Field names may be specified explicitly (IdentifierList) or
implicitly (AnonymousField).
Within a struct, non-<a href="#Blank_identifier">blank</a> field names must
be unique.
be <a href="#Uniqueness_of_identifiers">unique</a>.
</p>
<pre class="ebnf">
@ -1074,7 +1075,8 @@ InterfaceTypeName = TypeName .
</pre>
<p>
As with all method sets, in an interface type, each method must have a unique name.
As with all method sets, in an interface type, each method must have a
<a href="#Uniqueness_of_identifiers">unique</a> name.
</p>
<pre>
@ -1538,10 +1540,19 @@ the body of any nested function.
</p>
<h3 id="Blank_identifier">Blank identifier</h3>
<p>
The <i>blank identifier</i>, represented by the underscore character <code>_</code>, may be used in a declaration like
any other identifier but the declaration does not introduce a new binding.
</p>
<h3 id="Predeclared_identifiers">Predeclared identifiers</h3>
<p>
The following identifiers are implicitly declared in the universe block:
The following identifiers are implicitly declared in the
<a href="#Blocks">universe block</a>:
</p>
<pre class="grammar">
Types:
@ -1564,28 +1575,31 @@ Functions:
<h3 id="Exported_identifiers">Exported identifiers</h3>
<p>
An identifier may be <i>exported</i> to permit access to it from another package
using a <a href="#Qualified_identifiers">qualified identifier</a>. An identifier
is exported if both:
An identifier may be <i>exported</i> to permit access to it from another package.
An identifier is exported if both:
</p>
<ol>
<li>the first character of the identifier's name is a Unicode upper case letter (Unicode class "Lu"); and</li>
<li>the identifier is declared in the <a href="#Blocks">package block</a> or denotes a field or method of a type
declared in that block.</li>
<li>the first character of the identifier's name is a Unicode upper case
letter (Unicode class "Lu"); and</li>
<li>the identifier is declared in the <a href="#Blocks">package block</a>
or it is a <a href="#Struct_types">field name</a> or
<a href="#MethodName">method name</a>.</li>
</ol>
<p>
All other identifiers are not exported.
</p>
<h3 id="Blank_identifier">Blank identifier</h3>
<h3 id="Uniqueness_of_identifiers">Uniqueness of identifiers</h3>
<p>
The <i>blank identifier</i>, represented by the underscore character <code>_</code>, may be used in a declaration like
any other identifier but the declaration does not introduce a new binding.
Given a set of identifiers, an identifier is called <i>unique</i> if it is
<i>different</i> from every other in the set.
Two identifiers are different if they are spelled differently, or if they
appear in different <a href="#Packages">packages</a> and are not
<a href="Exported_identifiers">exported</a>. Otherwise, they are the same.
</p>
<h3 id="Constant_declarations">Constant declarations</h3>
<p>
@ -1942,7 +1956,7 @@ is visible only within selectors for that type.
<p>
For a base type, the non-<a href="#Blank_identifier">blank</a> names of
methods bound to it must be unique.
methods bound to it must be <a href="#Uniqueness_of_identifiers">unique</a>.
If the base type is a <a href="#Struct_types">struct type</a>,
the non-blank method and field names must be distinct.
</p>
@ -2022,12 +2036,12 @@ QualifiedIdent = [ PackageName "." ] identifier .
<p>
A qualified identifier accesses an identifier in a different package, which
must be <a href="#Import_declarations">imported</a>.
The identifier must be <a href="#Exported_identifiers">exported</a> by that
package, which means that it must begin with a Unicode upper case letter.
The identifier must be <a href="#Exported_identifiers">exported</a> and
declared in the <a href="#Blocks">package block</a> of that package.
</p>
<pre>
math.Sin
math.Sin // denotes the Sin function in package math
</pre>
<h3 id="Composite_literals">Composite literals</h3>
@ -2332,8 +2346,8 @@ where <code>T</code> is not an interface type,
<code>x.f</code> denotes the field or method at the shallowest depth
in <code>T</code> where there
is such an <code>f</code>.
If there is not exactly one <code>f</code> with shallowest depth, the selector
expression is illegal.
If there is not exactly <a href="#Uniqueness_of_identifiers">one <code>f</code></a>
with shallowest depth, the selector expression is illegal.
</li>
<li>
For a variable <code>x</code> of type <code>I</code>
@ -5070,11 +5084,12 @@ An implementation may require that all source files for a package inhabit the sa
<h3 id="Import_declarations">Import declarations</h3>
<p>
An import declaration states that the source file containing the
declaration uses identifiers
<a href="#Exported_identifiers">exported</a> by the <i>imported</i>
package and enables access to them. The import names an
identifier (PackageName) to be used for access and an ImportPath
An import declaration states that the source file containing the declaration
depends on functionality of the <i>imported</i> package
(<a href="#Program_initialization_and_execution">§Program initialization and execution</a>)
and it enables access to <a href="#Exported_identifiers">exported</a> identifiers
of that package.
The import names an identifier (PackageName) to be used for access and an ImportPath
that specifies the package to be imported.
</p>
@ -5086,13 +5101,14 @@ ImportPath = string_lit .
<p>
The PackageName is used in <a href="#Qualified_identifiers">qualified identifiers</a>
to access the exported identifiers of the package within the importing source file.
to access exported identifiers of the package within the importing source file.
It is declared in the <a href="#Blocks">file block</a>.
If the PackageName is omitted, it defaults to the identifier specified in the
<a href="#Package_clause">package clause</a> of the imported package.
If an explicit period (<code>.</code>) appears instead of a name, all the
package's exported identifiers will be declared in the current file's
file block and can be accessed without a qualifier.
package's exported identifiers declared in that package's
<a href="#Blocks">package block</a> will be declared in the importing source
file's file block and can be accessed without a qualifier.
</p>
<p>