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spec: clarify iteration variable type for range over integer

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Also: report language version (plus date) in spec header.

Fixes #65137.

Change-Id: I4f1d220d5922c40a36264df2d0a7bb7cd0756bac
Reviewed-on: https://go-review.googlesource.com/c/go/+/557596
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
This commit is contained in:
Robert Griesemer 2024-01-22 15:46:01 -08:00
parent c2dbbe4e94
commit 41d6687084
1 changed files with 25 additions and 13 deletions
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38
doc/go_spec.html
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@ -1,6 +1,6 @@
<!--{
"Title": "The Go Programming Language Specification",
"Subtitle": "Version of Dec 27, 2023",
"Subtitle": "Language version go1.22 (Jan 30, 2023)",
"Path": "/ref/spec"
}-->
@ -6661,7 +6661,7 @@ array or slice a [n]E, *[n]E, or []E index i int a[i] E
string s string type index i int see below rune
map m map[K]V key k K m[k] V
channel c chan E, &lt;-chan E element e E
integer n integer type I value i I
integer n integer type value i see below
</pre>
<ol>
@ -6703,26 +6703,33 @@ is <code>nil</code>, the range expression blocks forever.
<li>
For an integer value <code>n</code>, the iteration values 0 through <code>n-1</code>
are produced in increasing order, with the same type as <code>n</code>.
are produced in increasing order.
If <code>n</code> &lt= 0, the loop does not run any iterations.
</li>
</ol>
<p>
The iteration values are assigned to the respective
iteration variables as in an <a href="#Assignment_statements">assignment statement</a>.
</p>
<p>
The iteration variables may be declared by the "range" clause using a form of
<a href="#Short_variable_declarations">short variable declaration</a>
(<code>:=</code>).
In this case their types are set to the types of the respective iteration values
and their <a href="#Declarations_and_scope">scope</a> is the block of the "for" statement;
each iteration has its own separate variables [<a href="#Go_1.22">Go 1.22</a>]
In this case their <a href="#Declarations_and_scope">scope</a> is the block of the "for" statement
and each iteration has its own new variables [<a href="#Go_1.22">Go 1.22</a>]
(see also <a href="#For_clause">"for" statements with a ForClause</a>).
If the iteration variables are declared outside the “for” statement,
after execution their values will be those of the last iteration.
If the range expression is a (possibly untyped) integer expression <code>n</code>,
the variable has the same type as if it was
<a href="#Variable_declarations">declared</a> with initialization
expression <code>n</code>.
Otherwise, the variables have the types of their respective iteration values.
</p>
<p>
If the iteration variables are not explicitly declared by the "range" clause,
they must be preexisting.
In this case, the iteration values are assigned to the respective variables
as in an <a href="#Assignment_statements">assignment statement</a>.
If the range expression is a (possibly untyped) integer expression <code>n</code>,
<code>n</code> too must be <a href="#Assignability">assignable</a> to the iteration variable;
if there is no iteration variable, <code>n</code> must be assignable to <code>int</code>.
</p>
<pre>
@ -6765,6 +6772,11 @@ for i := range 10 {
// type of i is int (default type for untyped constant 10)
f(i)
}
// invalid: 256 cannot be assigned to uint8
var u uint8
for u = range 256 {
}
</pre>