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go/doc/go1.22.html
Joe Tsai c700c23cef reflect: make Value.IsZero identical to v == zero
The upcoming built-in zero value provides an idiomatic way
to test for zero by comparing to the zero literal: v == zero.

The reflect package is meant to provide a programmatic way to perform
operations that the Go language itself provides.
Thus, it seems prudent that reflect.ValueOf(&v).Elem().IsZero() is
identical to v == zero.

This change alters the behavior of Value.IsZero in two concrete ways:
* negative zero is identical to zero
* blank fields in a struct are ignored

Prior to this change, we were already in an inconsistent state
due to a regression introduced by CL 411478.
The new behavior was already the case for comparable composite types.
This change makes it consistent for all other types
(in particular incomparable composite types and standalone numbers).

Updates #61372
Fixes #61827

Change-Id: Id23fb97eb3b8921417cc75a1d3ead963e22dc3d9
Reviewed-on: https://go-review.googlesource.com/c/go/+/517777
Reviewed-by: Russ Cox <rsc@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
2023-09-01 23:20:30 +00:00

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<!--{
"Title": "Go 1.22 Release Notes",
"Path": "/doc/go1.22"
}-->
<!--
NOTE: In this document and others in this directory, the convention is to
set fixed-width phrases with non-fixed-width spaces, as in
<code>hello</code> <code>world</code>.
Do not send CLs removing the interior tags from such phrases.
-->
<style>
main ul li { margin: 0.5em 0; }
</style>
<h2 id="introduction">DRAFT RELEASE NOTES — Introduction to Go 1.22</h2>
<p>
<strong>
Go 1.22 is not yet released. These are work-in-progress
release notes. Go 1.22 is expected to be released in February 2024.
</strong>
</p>
<h2 id="language">Changes to the language</h2>
<p>
TODO: complete this section
</p>
<h2 id="tools">Tools</h2>
<h3 id="go-command">Go command</h3>
<p>
TODO: complete this section, or delete if not needed
</p>
<h3 id="cgo">Cgo</h3>
<p><!-- CL 497837 --> The special comment that precedes
<code>import</code> <code>"C"</code> may now include two
new <code>#cgo</code> directives.
<ul>
<li>
<code>#cgo</code> <code>noescape</code> <code>cFunctionName</code>
tells cgo that Go pointers passed to the C function
<code>cFunctionName</code> do not escape.
</li>
<li>
<code>#cgo</code> <code>nocallback</code> <code>cFunctionName</code>
tells cgo that the C function <code>cFunctionName</code> does
not call any Go functions.
</li>
</ul>
See <a href="/cmd/cgo#hdr-Optimizing_calls_of_C_code">the <code>cgo</code>
documentation</a> for more details.
</p>
<h2 id="runtime">Runtime</h2>
<p>
TODO: complete this section, or delete if not needed
</p>
<h2 id="compiler">Compiler</h2>
<p>
TODO: complete this section, or delete if not needed
</p>
<h2 id="linker">Linker</h2>
<p>
TODO: complete this section, or delete if not needed
</p>
<h2 id="library">Core library</h2>
<h3 id="minor_library_changes">Minor changes to the library</h3>
<p>
As always, there are various minor changes and updates to the library,
made with the Go 1 <a href="/doc/go1compat">promise of compatibility</a>
in mind.
There are also various performance improvements, not enumerated here.
</p>
<p>
TODO: complete this section
</p>
<dl id="database/sql"><dt><a href="/pkg/database/sql/">database/sql</a></dt>
<dd>
<p><!-- https://go.dev/issue/60370, CL 501700 -->
The new <a href="/pkg/database/sql/#Null"><code>Null[T]</code></a> type
provide a way to scan nullable columns for any column types.
</p>
</dd>
</dl>
<dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt>
<dd>
<p><!-- https://go.dev/issue/61827, CL 517777 -->
The <a href="/pkg/reflect/#Value.IsZero"><code>Value.IsZero</code></a>
method will now return true for a floating-point or complex
negative zero, and will return true for a struct value if a
blank field (a field named <code>_</code>) somehow has a
non-zero value.
These changes make <code>IsZero</code> consistent with comparing
a value to zero using the languague <code>==</code> operator.
</p>
</dd>
</dl>
<h2 id="ports">Ports</h2>
<p>
TODO: complete this section, or delete if not needed
</p>