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spec: remove special int rule for shifts

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The rule is not concistently followed by gc.
It appears that gccgo is ignoring it. go/types
does not implement this rule. However, both
gccgo and now go/types can compile/type-check
the entire std library (and thus all the shift
expressions occuring in it) w/o errors. For
more details see the discussion in issue 4883.

Fixes #4880.
Fixes #4881.
Fixes #4883.

R=rsc, r, iant, ken, ken, mtj, rogpeppe
CC=golang-dev
https://golang.org/cl/7707043
This commit is contained in:
Robert Griesemer 2013-03-15 13:55:50 -07:00
parent 7b7619626a
commit 58e21ddaf9
1 changed files with 5 additions and 5 deletions
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10
doc/go_spec.html
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@ -1,6 +1,6 @@
<!--{
"Title": "The Go Programming Language Specification",
"Subtitle": "Version of March 12, 2013",
"Subtitle": "Version of March 15, 2013",
"Path": "/ref/spec"
}-->
@ -2905,9 +2905,7 @@ The right operand in a shift expression must have unsigned integer type
or be an untyped constant that can be converted to unsigned integer type.
If the left operand of a non-constant shift expression is an untyped constant,
the type of the constant is what it would be if the shift expression were
replaced by its left operand alone; the type is <code>int</code> if it cannot
be determined from the context (for instance, if the shift expression is an
operand in a comparison against an untyped constant).
replaced by its left operand alone.
</p>
<pre>
@ -2916,10 +2914,12 @@ var i = 1&lt;&lt;s // 1 has type int
var j int32 = 1&lt;&lt;s // 1 has type int32; j == 0
var k = uint64(1&lt;&lt;s) // 1 has type uint64; k == 1&lt;&lt;33
var m int = 1.0&lt;&lt;s // 1.0 has type int
var n = 1.0&lt;&lt;s != 0 // 1.0 has type int; n == false if ints are 32bits in size
var n = 1.0&lt;&lt;s != i // 1.0 has type int; n == false if ints are 32bits in size
var o = 1&lt;&lt;s == 2&lt;&lt;s // 1 and 2 have type int; o == true if ints are 32bits in size
var p = 1&lt;&lt;s == 1&lt;&lt;33 // illegal if ints are 32bits in size: 1 has type int, but 1&lt;&lt;33 overflows int
var u = 1.0&lt;&lt;s // illegal: 1.0 has type float64, cannot shift
var u1 = 1.0&lt;&lt;s != 0 // illegal: 1.0 has type float64, cannot shift
var u2 = 1&lt;&lt;s != 1.0 // illegal: 1 has type float64, cannot shift
var v float32 = 1&lt;&lt;s // illegal: 1 has type float32, cannot shift
var w int64 = 1.0&lt;&lt;33 // 1.0&lt;&lt;33 is a constant shift expression
</pre>