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spec: only require parens around ambiguous conversions

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This is documenting the status quo. The previous cleanup
added this language as an implementation restriction, but
at least for now it is really part of the language proper.

Fixes #4605.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/7305071
This commit is contained in:
Russ Cox 2013-02-11 07:48:14 -05:00
parent 7576179aa3
commit 71c941b6f6
1 changed files with 8 additions and 10 deletions
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18
doc/go_spec.html
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@ -3448,16 +3448,20 @@ Conversion = Type "(" Expression [ "," ] ")" .
<p>
If the type starts with the operator <code>*</code> or <code>&lt;-</code>,
or the keyword <code>func</code>, it must be parenthesized:
or if the type starts with the keyword <code>func</code>
and has no result list, it must be parenthesized when
necessary to avoid ambiguity:
</p>
<pre>
*Point(p) // same as *(Point(p))
(*Point)(p) // p is converted to (*Point)
(*Point)(p) // p is converted to *Point
&lt;-chan int(c) // same as &lt;-(chan int(c))
(&lt;-chan int)(c) // c is converted to (&lt;-chan int)
(&lt;-chan int)(c) // c is converted to &lt;-chan int
func()(x) // function signature func() x
(func())(x) // x is converted to (func())
(func())(x) // x is converted to func()
(func() int)(x) // x is converted to func() int
func() int(x) // x is converted to func() int (unambiguous)
</pre>
<p>
@ -3553,12 +3557,6 @@ implements this functionality under
restricted circumstances.
</p>
<p>
Implementation restriction: For backward-compatibility with the Go 1 language
specification, a compiler may accept non-parenthesized literal function types
in conversions where the syntax is unambiguous.
</p>
<h4>Conversions between numeric types</h4>
<p>