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doc/go1.2.html: some library changes (fmt, template)
Also link it to the landing page for docs. R=golang-dev, adg CC=golang-dev https://golang.org/cl/13652045
This commit is contained in:
Rob Pike
parent
ff416a3f19
commit
a97a7c5eb6
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@ -88,6 +88,12 @@ A list of significant changes in Go 1.1, with instructions for updating your
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code where necessary.
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</p>
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<h3 id="go1.2notes"><a href="/doc/go1.2.html">Go 1.2 Release Notes</a></h3>
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<p>
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A list of significant changes in Go 1.2, with instructions for updating your
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code where necessary.
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</p>
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<h3 id="go1compat"><a href="/doc/go1compat.html">Go 1 and the Future of Go Programs</a></h3>
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<p>
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What Go 1 defines and the backwards-compatibility guarantees one can expect as
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228
doc/go1.2.html
228
doc/go1.2.html
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@ -163,7 +163,7 @@ no client code depends on the godoc sources and no updating is required.
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</p>
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<p>
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The binary distributions available from <a href="http://golang.org>golang.org</a>
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The binary distributions available from <a href="http://golang.org">golang.org</a>
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include a godoc binary, so users of these distributions are unaffected.
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</p>
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@ -269,83 +269,176 @@ to list them all here, but the following major changes are worth noting:
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</p>
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<ul>
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<li>compress/bzip2: faster decompression by 30% (CL 9915043).
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<li>compress/bzip2: TODO faster decompression by 30% (CL 9915043).
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</li>
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<li>crypto/des: 5x faster encoding/decoding (CL 11874043, 12072045).
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<li>crypto/des: TODO 5x faster encoding/decoding (CL 11874043, 12072045).
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</li>
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<li>encoding/json: faster encoding (CL 9129044).
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<li>encoding/json: TODO faster encoding (CL 9129044).
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</li>
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<li>net: improve windows performance by up to 30% (CL 8670044).
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<li>net: TODO improve windows performance by up to 30% (CL 8670044).
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</li>
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<li>net: improve performance on BSD by up to 30% (CL 8264043, 12927048, 13080043).
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<li>net: TODO improve performance on BSD by up to 30% (CL 8264043, 12927048, 13080043).
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</li>
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</ul>
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<h2 id="library">Changes to the standard library</h2>
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<h3 id="foo_bar">foo.Bar</h3>
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<h3 id="archive_tar_zip">The archive/tar and archive/zip packages</h3>
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<p>
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TODO: choose which to call out
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<font color=red>
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The various routines to scan textual input in the
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<a href="/pkg/bufio/"><code>bufio</code></a>
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package,
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<a href="/pkg/bufio/#Reader.ReadBytes"><code>ReadBytes</code></a>,
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<a href="/pkg/bufio/#Reader.ReadString"><code>ReadString</code></a>
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and particularly
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<a href="/pkg/bufio/#Reader.ReadLine"><code>ReadLine</code></a>,
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are needlessly complex to use for simple purposes.
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In Go 1.1, a new type,
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<a href="/pkg/bufio/#Scanner"><code>Scanner</code></a>,
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has been added to make it easier to do simple tasks such as
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read the input as a sequence of lines or space-delimited words.
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It simplifies the problem by terminating the scan on problematic
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input such as pathologically long lines, and having a simple
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default: line-oriented input, with each line stripped of its terminator.
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Here is code to reproduce the input a line at a time:
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</font>
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<p>
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<font color=red>
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<em>Updating</em>:
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To correct breakage caused by the new struct field,
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<code>go fix</code> will rewrite code to add tags for these types.
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More generally, <code>go vet</code> will identify composite literals that
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should be revised to use field tags.
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</font>
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Breaking change: TODO
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archive/tar,archive/zip: fix os.FileInfo implementation to provide base name only (CL 13118043).
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</p>
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<ul>
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<h3 id="encoding">The new encoding package</h3>
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<li>
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Breaking change:
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archive/tar,archive/zip: fix os.FileInfo implementation to provide base name only (CL 13118043).
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</li>
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<p>
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encoding: TODO new package defining generic encoding interfaces (CL 12541051).
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</p>
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<li>
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encoding: new package defining generic encoding interfaces (CL 12541051).
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</li>
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<h3 id="fmt_indexed_arguments">The fmt package</h3>
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<li>
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fmt: indexed access to arguments in Printf etc. (CL 9680043).
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</li>
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<p>
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The <a href="/pkg/fmt/"><code>fmt</code></a> package's formatted print
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routines such as <a href="/pkg/fmt/#Printf"><code>Printf</code></a>
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now allow the data items to be printed to be accessed in arbitrary order
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by using an indexing operation in the formatting specifications.
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Wherever an argument is to be fetched from the argument list for formatting,
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either as the value to be formatted or as a width or specification integer,
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a new optional indexing notation <code>[</code><em>n</em><code>]</code>
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fetches argument <em>n</em> instead.
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The value of <em>n</em> is 1-indexed.
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After such an indexing operating, the next argument to be fetched by normal
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processing will be <em>n</em>+1.
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</p>
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<li>
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sync/atomic: add Swap functions (CL 12670045).
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</li>
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<li>
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text/template: add comparison functions (CL 13091045).
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</li>
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<p>
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For example, the normal <code>Printf</code> call
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</p>
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<li>
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text/template: allow {{"{{"}}else if ... {{"}}"}} to simplify if chains (CL 13327043).
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</li>
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</ul>
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<pre>
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fmt.Sprintf("%c %c %c\n", 'a', 'b', 'c')
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</pre>
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<p>
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would create the string <code>"a b c"</code>, but with indexing operations like this,
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</p>
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<pre>
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fmt.Sprintf("%[3]c %[1]c %c\n", 'a', 'b', 'c')
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</pre>
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<p>
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the result is "<code>"c a b"</code>. The <code>[3]</code> index accesses the third formatting
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argument, whch is <code>'c'</code>, <code>[1]</code> accesses the first, <code>'a'</code>,
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and then the next fetch accesses the argument following that one, <code>'b'</code>.
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</p>
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<p>
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The motivation for this feature is programmable format statements to access
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the arguments in different order for localization, but it has other uses:
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</p>
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<pre>
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log.Printf("trace: value %v of type %[1]T\n", expensiveFunction(a.b[c]))
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</pre>
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<p>
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<em>Updating</em>: The change to the syntax of format specifications
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is strictly backwards compatible, so it affects no working programs.
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</p>
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<h3 id="text_template">The text/template and html/template packages</h3>
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<p>
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The
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<a href="/pkg/text/template/"><code>text/template</code></a> package
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has a couple of changes in Go 1.2, both of which are also mirrored in the
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<a href="/pkg/html/template/"><code>html/template</code></a> package.
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</p>
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<p>
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First, there are new default functions for comparing basic types.
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The functions are listed in this table, which shows their names and
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the associated familiar comparison operator.
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</p>
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<table cellpadding="0" summary="Template comparison functions">
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<tr>
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<th width="50"></th><th width="100">Name</th> <th width="50">Operator</th>
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</tr>
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<tr>
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<td></td><td><code>eq</code></td> <td><code>==</code></td>
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</tr>
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<tr>
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<td></td><td><code>ne</code></td> <td><code>!=</code></td>
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</tr>
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<tr>
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<td></td><td><code>lt</code></td> <td><code><</code></td>
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</tr>
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<tr>
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<td></td><td><code>le</code></td> <td><code><=</code></td>
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</tr>
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<tr>
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<td></td><td><code>gt</code></td> <td><code>></code></td>
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</tr>
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<tr>
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<td></td><td><code>ge</code></td> <td><code>>=</code></td>
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</tr>
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</table>
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<p>
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These functions behave slightly differently from the corresponding Go operators.
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First, they operate only on basic types (<code>bool</code>, <code>int</code>,
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<code>float64</code>, <code>string</code>, etc.).
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(Go allows comparison of arrays and structs as well, under some circumstances.)
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Second, values can be compared as long as they are the same sort of value:
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any signed integer value can be compared to any other signed integer value for example. (Go
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does not permit comparing an <code>int8</code> and an <code>int16</code>).
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Finally, the <code>eq</code> function (only) allows comparison of the first
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argument with one or more following arguments. The template in this example,
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</p>
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<pre>
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{{"{{"}}if eq .A 1 2 3 {{"}}"}} equal {{"{{"}}else{{"}}"}} not equal {{"{{"}}end{{"}}"}}
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</pre>
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<p>
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reports "equal" if <code>.A</code> is equal to <em>any</em> of 1, 2, or 3.
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</p>
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<p>
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The second change is that a small addition to the grammar makes "if else if" chains easier to write.
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Instead of writing,
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</p>
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<pre>
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{{"{{"}}if eq .A 1{{"}}"}} X {{"{{"}}else{{"}}"}} {{"{{"}}if eq .A 2{{"}}"}} Y {{"{{"}}end{{"}}"}} {{"{{"}}end{{"}}"}}
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</pre>
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<p>
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one can fold the second "if" into the "else" and have only one "end", like this:
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</p>
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<pre>
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{{"{{"}}if eq .A 1{{"}}"}} X {{"{{"}}else if eq .A 2{{"}}"}} Y {{"{{"}}end{{"}}"}}
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</pre>
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<p>
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The two forms are identical in effect; the difference is just in the syntax.
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</p>
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<p>
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<em>Updating</em>: Neither change affects existing programs. Those that
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already define functions called <code>eq</code> and so on through a function
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map are unaffected because the associated function map will override the new
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default function definitions.
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</p>
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<h3 id="minor_library_changes">Minor changes to the library</h3>
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@ -556,19 +649,19 @@ so that less intermediate buffering is required in general.
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</li>
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<li>
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net: new build tag netgo for building a pure Go net package (CL 7100050).
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net: TODO new build tag netgo for building a pure Go net package (CL 7100050).
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</li>
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<li>
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net/http: don't allow sending invalid cookie lines (CL 12204043).
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net/http: TODO don't allow sending invalid cookie lines (CL 12204043).
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</li>
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<li>
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net/http: allow ReadResponse with nil *Request parameter (CL 9821043).
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net/http: TODO allow ReadResponse with nil *Request parameter (CL 9821043).
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</li>
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<li>
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net/http: allow responses to HEAD requests, detect type and length (CL 12583043).
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net/http: TODO allow responses to HEAD requests, detect type and length (CL 12583043).
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</li>
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<li>
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@ -591,6 +684,21 @@ an <a href="/pkg/strings/#IndexByte"><code>IndexByte</code></a>
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function for consistency with the <a href="/pkg/bytes/"><code>bytes</code></a> package.
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</li>
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<li>
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The <a href="/pkg/sync/atomic/"><code>sync/atomic</code></a> package
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adds a new set of swap functions that atomically exchange the argument with the
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value stored in the pointer, returning the old value.
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The functions are
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<a href="/pkg/sync/atomic/#SwapInt32"><code>SwapInt32</code></a>,
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<a href="/pkg/sync/atomic/#SwapInt64"><code>SwapInt64</code></a>,
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<a href="/pkg/sync/atomic/#SwapUint32"><code>SwapUint32</code></a>,
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<a href="/pkg/sync/atomic/#SwapUint64"><code>SwapUint64</code></a>,
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<a href="/pkg/sync/atomic/#SwapUintptr"><code>SwapUintptr</code></a>,
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and
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<a href="/pkg/sync/atomic/#SwapPointer"><code>SwapPointer</code></a>,
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which swaps an <code>unsafe.Pointer</code>.
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</li>
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<li>
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syscall: implemented Sendfile for Darwin, added Syscall9 for Darwin/amd64 (CL 10980043).
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</li>
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