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doc: add type aliases to go1.9.html
Updates #20587 Change-Id: I5df603505ae1d4b65687bec1e973a4ab318b34f1 Reviewed-on: https://go-review.googlesource.com/45014 Reviewed-by: Robert Griesemer <gri@golang.org> Reviewed-by: Rob Pike <r@golang.org>
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@ -23,12 +23,18 @@ ul li { margin: 0.5em 0; }
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</strong></p>
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<p>
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The latest Go release, version 1.9, arrives six months after <a href="go1.8">Go 1.8</a>
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and is the tenth release in the <a href="https://golang.org/doc/devel/release.html">Go 1.x series</a>.
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Most of its changes are in the implementation of the toolchain, runtime, and libraries.
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There are no changes to the language specification.
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As always, the release maintains the Go 1 <a href="/doc/go1compat.html">promise of compatibility</a>.
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We expect almost all Go programs to continue to compile and run as before.
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The latest Go release, version 1.9, arrives six months
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after <a href="go1.8">Go 1.8</a> and is the tenth release in
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the <a href="https://golang.org/doc/devel/release.html">Go 1.x
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series</a>.
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There is one <a href="#language">change to the language</a>, adding
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support for type aliases.
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Most of the changes are in the implementation of the toolchain,
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runtime, and libraries.
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As always, the release maintains the Go 1
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<a href="/doc/go1compat.html">promise of compatibility</a>.
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We expect almost all Go programs to continue to compile and run as
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before.
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</p>
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<p>
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@ -39,6 +45,29 @@ ul li { margin: 0.5em 0; }
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and includes a new <a href="#math-bits">bit manipulation package</a>.
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</p>
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<h2 id="language">Changes to the language</h2>
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<p>
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There is one change to the language.
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Go now supports type aliases to support gradual code repair while
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moving a type between packages.
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The <a href="https://golang.org/design/18130-type-alias">type alias
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design document</a>
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and <a href="https://talks.golang.org/2016/refactor.article">an
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article on refactoring</a> cover the problem in detail.
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In short, a type alias declaration has the form:
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</p>
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<pre>
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type T1 = T2
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</pre>
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<p>
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This declaration introduces an alias name <code>T1</code>—an
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alternate spelling—for the type denoted by <code>T2</code>; that is,
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both <code>T1</code> and <code>T2</code> denote the same type.
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</p>
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<h2 id="ports">Ports</h2>
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<p>
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@ -147,7 +176,7 @@ ul li { margin: 0.5em 0; }
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The
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new <a href="/pkg/testing/#T.Helper"><code>(*T).Helper</code></a>
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an <a href="/pkg/testing/#B.Helper"><code>(*B).Helper</code></a>
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methods marks the calling function as a test helper function. When
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methods mark the calling function as a test helper function. When
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printing file and line information, that function will be skipped.
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This permits writing test helper functions while still having useful
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line numbers for users.
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