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spec: clarify prose for range over numeric range expressions 

Fixes #66967.

Change-Id: I7b9d62dcb83bad60b2ce74e2e2bf1a36c6a8ae38
Reviewed-on: https://go-review.googlesource.com/c/go/+/581256
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
This commit is contained in:
Robert Griesemer 2024-04-23 17:22:02 -07:00
parent 1ca31eac40
commit 5419f652b6
1 changed files with 22 additions and 16 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": "Language version go1.22 (April 24, 2024)",
"Subtitle": "Language version go1.22 (April 25, 2024)",
"Path": "/ref/spec"
}-->
@ -6656,13 +6656,13 @@ if the respective iteration variables are present:
</p>
<pre class="grammar">
Range expression 1st value 2nd value
Range expression 1st value 2nd value
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 value i see below
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 value n integer type, or untyped int value i see below
</pre>
<ol>
@ -6703,8 +6703,17 @@ is <code>nil</code>, the range expression blocks forever.
</li>
<li>
For an integer value <code>n</code>, the iteration values 0 through <code>n-1</code>
For an integer value <code>n</code>, where <code>n</code> is of <a href="#Numeric_types">integer type</a>
or an untyped <a href="#Constants">integer constant</a>, the iteration values 0 through <code>n-1</code>
are produced in increasing order.
If <code>n</code> is of integer type, the iteration values have that same type.
Otherwise, the type of <code>n</code> is determined as if it were assigned to the
iteration variable.
Specifically:
if the iteration variable is preexisting, the type of the iteration values is the type of the iteration
variable, which must be of integer type.
Otherwise, if the iteration variable is declared by the "range" clause or is absent,
the type of the iteration values is the <a href="#Constants">default type</a> for <code>n</code>.
If <code>n</code> &lt= 0, the loop does not run any iterations.
</li>
</ol>
@ -6716,11 +6725,7 @@ The iteration variables may be declared by the "range" clause using a form of
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 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.
The variables have the types of their respective iteration values.
</p>
<p>
@ -6728,9 +6733,6 @@ 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>
@ -6778,6 +6780,10 @@ for i := range 10 {
var u uint8
for u = range 256 {
}
// invalid: 1e3 is a floating-point constant
for range 1e3 {
}
</pre>