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spec: corrections to various sections
- fix definition of "specific types" and add more examples - state that a parameterized function must be instantiated when used as a function value - remove duplicate word ("can can" -> "can") Thanks to @danscales for finding these. Change-Id: Ideb41efc35a3e67694d3bc97e462454feae37c44 Reviewed-on: https://go-review.googlesource.com/c/go/+/367394 Trust: Robert Griesemer <gri@golang.org> Trust: Dan Scales <danscales@google.com> Reviewed-by: Ian Lance Taylor <iant@golang.org> Reviewed-by: Dan Scales <danscales@google.com>
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@ -1,6 +1,6 @@
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<!--{
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"Title": "The Go Programming Language Specification - Go 1.18 Draft (incomplete)",
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"Subtitle": "Version of Nov 24, 2021",
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"Subtitle": "Version of Nov 29, 2021",
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"Path": "/ref/spec"
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}-->
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@ -1971,39 +1971,38 @@ x T x is not representable by a value of T because
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<p>
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An interface specification which contains <a href="#Interface_types">type elements</a>
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that are not interface types defines a (possibly empty) set of <i>specific types</i>.
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defines a (possibly empty) set of <i>specific types</i>.
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Loosely speaking, these are the types <code>T</code> that appear in the
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interface definition in terms of the form <code>T</code>, <code>~T</code>,
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or in unions of such terms.
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</p>
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<p>
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More precisely, for a given interface, the set of specific types is defined as follows:
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More precisely, for a given interface, the set 𝑆 of specific types is defined as follows:
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</p>
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<ul>
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<li>The set of specific types of the empty interface is the empty set.
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<li>For an interface with no type elements, 𝑆 is the empty set.
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</li>
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<li>The set of specific types of a non-empty interface is the intersection
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of the specific types of its interface elements.
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<li>For an interface with type elements, 𝑆 is the intersection
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of the specific types of its type elements.
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</li>
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<li>The set of specific types of a method specification is the empty set.
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<li>For a non-interface type term <code>T</code>
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or <code>~T</code>, 𝑆 is the set consisting of the type <code>T</code>.
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</li>
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<li>The set of specific types of a non-interface type term <code>T</code>
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or <code>~T</code> is the set consisting of the type <code>T</code>.
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</li>
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<li>The set of specific types of a <i>union</i> of terms
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<code>t<sub>1</sub>|t<sub>2</sub>|…|t<sub>n</sub></code>
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is the union of the specific types of the terms.
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<li>For a <i>union</i> of terms
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<code>t<sub>1</sub>|t<sub>2</sub>|…|t<sub>n</sub></code>,
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𝑆 is the union of the specific types of the terms.
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</li>
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</ul>
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<p>
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If the set of specific types is empty, the interface has <i>no specific types</i>.
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If 𝑆 is empty, the interface has <i>no specific types</i>.
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An interface may have specific types even if its <a href="#Interface_types">type set</a>
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is empty.
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</p>
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<p>
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@ -2019,6 +2018,8 @@ interface{ int } // int
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interface{ ~string } // string
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interface{ int|~string } // int, string
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interface{ Celsius|Kelvin } // Celsius, Kelvin
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interface{ int; m() } // int (but type set is empty because int has no method m)
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interface{ int; any } // no specific types (intersection is empty)
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interface{ int; string } // no specific types (intersection is empty)
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</pre>
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@ -3980,7 +3981,8 @@ pt.Scale(3.5) // method call with receiver pt
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<p>
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If <code>f</code> denotes a parameterized function, it must be
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<a href="#Instantiations">instantiated</a> before it can be called.
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<a href="#Instantiations">instantiated</a> before it can be called
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or used as a function value.
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</p>
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<p>
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@ -4807,7 +4809,7 @@ Only <code>V</code> is a type parameter and a value of each
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specific type of <code>V</code> can be converted to <code>T</code>.
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</li>
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<li>
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Only <code>T</code> is a type parameter and <code>x</code> can can be converted to each
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Only <code>T</code> is a type parameter and <code>x</code> can be converted to each
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specific type of <code>T</code>.
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</li>
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</ul>
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