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spec: document min and max built-ins

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For #59488.

Change-Id: I50f65216bf02b42c1e0619702833f4a6dbed8925
Reviewed-on: https://go-review.googlesource.com/c/go/+/498136
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
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Robert Griesemer 2023-05-24 13:23:14 -07:00 committed by Robert Griesemer
parent 01b5cce626
commit f9d114d0e8
1 changed files with 67 additions and 2 deletions
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doc/go_spec.html
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@ -1,6 +1,6 @@
<!--{
"Title": "The Go Programming Language Specification",
"Subtitle": "Version of May 24, 2023",
"Subtitle": "Version of May 25, 2023",
"Path": "/ref/spec"
}-->
@ -643,6 +643,7 @@ an identifier denoting a constant,
a <a href="#Constant_expressions">constant expression</a>,
a <a href="#Conversions">conversion</a> with a result that is a constant, or
the result value of some built-in functions such as
<code>min</code> or <code>max</code> applied to constant arguments,
<code>unsafe.Sizeof</code> applied to <a href="#Package_unsafe">certain values</a>,
<code>cap</code> or <code>len</code> applied to
<a href="#Length_and_capacity">some expressions</a>,
@ -2319,7 +2320,7 @@ Zero value:
Functions:
append cap clear close complex copy delete imag len
make new panic print println real recover
make max min new panic print println real recover
</pre>
<h3 id="Exported_identifiers">Exported identifiers</h3>
@ -7531,6 +7532,70 @@ The precise behavior is implementation-dependent.
</p>
<h3 id="Min_and_max">Min and max</h3>
<p>
The built-in functions <code>min</code> and <code>max</code> compute the
smallest&mdash;or largest, respectively&mdash;value of a fixed number of
arguments of <a href="#Comparison_operators">ordered types</a>.
There must be at least one argument.
</p>
<p>
The same type rules as for <a href="#Operators">operators</a> apply:
for <a href="#Comparison_operators">ordered</a> arguments <code>x</code> and
<code>y</code>, <code>min(x, y)</code> is valid if <code>x + y</code> is valid,
and the type of <code>min(x, y)</code> is the type of <code>x + y</code>
(and similarly for <code>max</code>).
If all arguments are constant, the result is constant.
</p>
<pre>
var x, y int
m := min(x) // m == x
m := min(x, y) // m is the smaller of x and y
m := max(x, y, 10) // m is the larger of x and y but at least 10
c := max(1, 2.0, 10) // c == 10.0 (floating-point kind)
f := max(0, float32(x)) // type of f is float32
var s []string
_ = min(s...) // invalid: slice arguments are not permitted
t := max("", "foo", "bar") // t == "foo" (string kind)
</pre>
<p>
For numeric arguments, <code>min</code> and <code>max</code> are
commutative and associative:
</p>
<pre>
min(x, y) == min(y, x)
min(x, y, z) == min(min(x, y), z) == min(x, min(y, z))
</pre>
<p>
For floating-point arguments negative zero, NaN, and infinity the following rules apply:
</p>
<pre>
x y min(x, y) max(x, y)
-0.0 0.0 -0.0 0.0 // negative zero is smaller than (non-negative) zero
-Inf y -Inf y // negative infinity is smaller than any other number
+Inf y y +Inf // positive infinity is larger than any other number
NaN y NaN NaN // if any argument is a NaN, the result is a NaN
</pre>
<p>
For string arguments the result for <code>min</code> is the first argument
with the smallest (or for <code>max</code>, largest) value,
compared lexically byte-wise:
</p>
<pre>
min(x, y) == if x <= y then x else y
min(x, y, z) == min(min(x, y), z)
</pre>
<h3 id="Allocation">Allocation</h3>
<p>