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spec: document numeric operations behavior for generic types

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Includes a few minor cosmetic changes.

Change-Id: I6c307d958b47d83671142688630ea7835168439f
Reviewed-on: https://go-review.googlesource.com/c/go/+/384622
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Robert Griesemer 2022-02-09 15:40:20 -08:00
parent 8ba3ad92eb
commit 3b8c716e0f
1 changed files with 36 additions and 7 deletions
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doc/go_spec.html
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@ -1,6 +1,6 @@
<!--{
"Title": "The Go Programming Language Specification - Go 1.18 Draft (incomplete)",
"Subtitle": "Version of Feb 9, 2022",
"Subtitle": "Version of Feb 10, 2022",
"Path": "/ref/spec"
}-->
@ -4752,7 +4752,7 @@ Arithmetic operators apply to numeric values and yield a result of the same
type as the first operand. The four standard arithmetic operators (<code>+</code>,
<code>-</code>, <code>*</code>, <code>/</code>) apply to
<a href="#Numeric_types">integer</a>, <a href="#Numeric_types">floating-point</a>, and
<a href="#Numeric_types">complex</a> types; <code>+</code> also applies to <a href="#String_types">strings</.
<a href="#Numeric_types">complex</a> types; <code>+</code> also applies to <a href="#String_types">strings</a>.
The bitwise logical and shift operators apply to integers only.
</p>
@ -4772,6 +4772,37 @@ The bitwise logical and shift operators apply to integers only.
&gt;&gt; right shift integer &gt;&gt; integer &gt;= 0
</pre>
<p>
Excluding shifts, if the operand type is a <a href="#Type_parameters">type parameter</a>,
it must have <a href="#Structure_of_interfaces">specific types</a>, and the operator must
apply to each specific type.
The operands are represented as values of the type argument that the type parameter
is <a href="#Instantiations">instantiated</a> with, and the operation is computed
with the precision of that type argument. For example, given the function:
</p>
<pre>
func dotProduct[F ~float32|~float64](v1, v2 []F) F {
var s F
for i, x := range v1 {
y := v2[i]
s += x * y
}
return s
}
</pre>
<p>
the the product <code>x * y</code> and the addition <code>s += x * y</code>
are computed with <code>float32</code> or <code>float64</code> precision,
respectively, depending on the type argument for <code>F</code>.
</p>
<p>
For shifts, the <a href="#Core_types">core type</a> of both operands must be
an integer.
</p>
<h4 id="Integer_operators">Integer operators</h4>
<p>
@ -4857,10 +4888,10 @@ follows:
<h4 id="Integer_overflow">Integer overflow</h4>
<p>
For unsigned integer values, the operations <code>+</code>,
For <a href="#Numeric_types">unsigned integer</a> values, the operations <code>+</code>,
<code>-</code>, <code>*</code>, and <code>&lt;&lt;</code> are
computed modulo 2<sup><i>n</i></sup>, where <i>n</i> is the bit width of
the <a href="#Numeric_types">unsigned integer</a>'s type.
the unsigned integer's type.
Loosely speaking, these unsigned integer operations
discard high bits upon overflow, and programs may rely on "wrap around".
</p>
@ -4875,7 +4906,6 @@ A compiler may not optimize code under the assumption that overflow does
not occur. For instance, it may not assume that <code>x &lt; x + 1</code> is always true.
</p>
<h4 id="Floating_point_operators">Floating-point operators</h4>
<p>
@ -4931,7 +4961,6 @@ s += " and good bye"
String addition creates a new string by concatenating the operands.
</p>
<h3 id="Comparison_operators">Comparison operators</h3>
<p>
@ -5220,7 +5249,7 @@ string(65.0) // illegal: 65.0 is not an integer constant
<p>
Converting a constant to a type parameter yields a <i>non-constant</i> value of that type,
with the value represented as a value of the type argument that the type parameter
is instantiated with.
is <a href="#Instantiations">instantiated</a> with.
For example, given the function:
</p>