code review 4515176: go spec: specify constant conversions

go spec: specify constant conversions

This is not a language change.

Added paragraphs specifying which conversions
yield results that are constants.

[gri, 2011-06-01 20:57:11]

Hello r@golang.org, rsc@golang.org, iant@golang.org, ken@golang.org (cc:
golang-dev@googlegroups.com),

I'd like you to review this change to
https://go.googlecode.com/hg/

[iant2, 2011-06-01 21:05:09]

LGTM

gri@golang.org writes:

> Reviewers: r, rsc, iant, ken2,
>
> Message:
> Hello r@golang.org, rsc@golang.org, iant@golang.org, ken@golang.org (cc:
> golang-dev@googlegroups.com),
>
> I'd like you to review this change to
> https://go.googlecode.com/hg/
>
>
> Description:
> go spec: specify constant conversions
>
> This is not a language change.
>
> Added paragraphs specifying which conversions
> yield results that are constants.
>
> Please review this at http://codereview.appspot.com/4515176/
>
> Affected files:
>   M doc/go_spec.html
>
>
> Index: doc/go_spec.html
> ===================================================================
> --- a/doc/go_spec.html
> +++ b/doc/go_spec.html
> @@ -1,5 +1,5 @@
>  <!-- title The Go Programming Language Specification -->
> -<!-- subtitle Version of May 24, 2011 -->
> +<!-- subtitle Version of June 1, 2011 -->
>
>  <!--
>  TODO
> @@ -529,7 +529,8 @@
>  <a href="#Character_literals">character</a>, or
>  <a href="#String_literals">string</a> literal,
>  an identifier denoting a constant,
> -a <a href="#Constant_expressions">constant expression</a>, or
> +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>unsafe.Sizeof</code> applied to any value,
>  <code>cap</code> or <code>len</code> applied to
> @@ -3265,6 +3266,28 @@
>  of <code>x</code>.
>  </p>
>
> +<p>
> +There is no linguistic mechanism to convert between pointers and integers.
> +The package <a href="#Package_unsafe"><code>unsafe</code></a>
> +implements this functionality under
> +restricted circumstances.
> +</p>
> +
> +<p>
> +The result of a conversion is a <a href="#Constants">constant</a> if
> +<code>x</code> is a constant and <code>T</code> is of boolean, numeric,
> +or string type.
> +</p>
> +
> +<pre>
> +uint(iota)               // iota value of type uint
> +float32(2.718281828)     // 2.718281828 of type float32
> +MyString("foo" + "bar")  // "foobar" of type MyString
> +string(0x266c)           // "♬" of type string
> +string([]byte{'a'})      // not a constant: []byte{'a'} is not a constant
> +(*int)(nil)              // not a constant: nil is not a constant,
> *int is not a boolean, numeric, or string type
> +</pre>
> +
>  <h4>Conversions between numeric types</h4>
>  <ol>
>  <li>
> @@ -3355,12 +3378,6 @@
>  </li>
>  </ol>
>
> -<p>
> -There is no linguistic mechanism to convert between pointers and integers.
> -The package <a href="#Package_unsafe"><code>unsafe</code></a>
> -implements this functionality under
> -restricted circumstances.
> -</p>
>
>  <h3 id="Constant_expressions">Constant expressions</h3>

[rsc, 2011-06-01 21:17:41]

LGTM

Maybe add string('x') before the string(0x266c).  Nice code point by the way.

[r, 2011-06-01 22:45:36]

LGTM

does it say somewhere that

int(3.2)

is illegal?

[gri, 2011-06-01 22:56:23]

ugh. not sure. will revisit.
- gri

On Wed, Jun 1, 2011 at 3:45 PM,  <r@golang.org> wrote:
> LGTM
>
> does it say somewhere that
>
> int(3.2)
>
> is illegal?
>
> http://codereview.appspot.com/4515176/
>

[gri, 2011-06-08 21:59:56]

PTAL.

This is the CL re: constant conversions. Previously, there was no
explicit language about conversions such as int(3.2).

Now:

- distinguish between constant and non-constant conversions
- have separate rules for each case
- added a few more illegal examples

- gri

On Wed, Jun 1, 2011 at 3:56 PM, Robert Griesemer <gri@golang.org> wrote:
> ugh. not sure. will revisit.
> - gri
>
> On Wed, Jun 1, 2011 at 3:45 PM,  <r@golang.org> wrote:
>> LGTM
>>
>> does it say somewhere that
>>
>> int(3.2)
>>
>> is illegal?
>>
>> http://codereview.appspot.com/4515176/
>>
>

[gri, 2011-06-08 23:52:47]

Here's the new text in the Conversions section:

http://godoc-test.prom.corp.google.com/doc/go_spec.html#Conversions

served freshly via app engine
- gri

On Wed, Jun 8, 2011 at 2:59 PM, Robert Griesemer <gri@golang.org> wrote:
> PTAL.
>
> This is the CL re: constant conversions. Previously, there was no
> explicit language about conversions such as int(3.2).
>
> Now:
>
> - distinguish between constant and non-constant conversions
> - have separate rules for each case
> - added a few more illegal examples
>
> - gri
>
> On Wed, Jun 1, 2011 at 3:56 PM, Robert Griesemer <gri@golang.org> wrote:
>> ugh. not sure. will revisit.
>> - gri
>>
>> On Wed, Jun 1, 2011 at 3:45 PM,  <r@golang.org> wrote:
>>> LGTM
>>>
>>> does it say somewhere that
>>>
>>> int(3.2)
>>>
>>> is illegal?
>>>
>>> http://codereview.appspot.com/4515176/
>>>
>>
>

[gri, 2011-06-13 16:54:03]

ping

On Wed, Jun 8, 2011 at 2:59 PM, Robert Griesemer <gri@golang.org> wrote:
> PTAL.
>
> This is the CL re: constant conversions. Previously, there was no
> explicit language about conversions such as int(3.2).
>
> Now:
>
> - distinguish between constant and non-constant conversions
> - have separate rules for each case
> - added a few more illegal examples
>
> - gri
>
> On Wed, Jun 1, 2011 at 3:56 PM, Robert Griesemer <gri@golang.org> wrote:
>> ugh. not sure. will revisit.
>> - gri
>>
>> On Wed, Jun 1, 2011 at 3:45 PM,  <r@golang.org> wrote:
>>> LGTM
>>>
>>> does it say somewhere that
>>>
>>> int(3.2)
>>>
>>> is illegal?
>>>
>>> http://codereview.appspot.com/4515176/
>>>
>>
>

[rsc, 2011-06-13 16:59:59]

LGTM

[r, 2011-06-13 23:37:59]

LGTM

[iant, 2011-06-13 23:42:21]

LGTM

[gri, 2011-06-13 23:47:38]

*** Submitted as http://code.google.com/p/go/source/detail?r=dc2faaa6c26a ***

go spec: specify constant conversions

This is not a language change.

Added paragraphs specifying which conversions
yield results that are constants.

R=r, rsc, iant, ken
CC=golang-dev
http://codereview.appspot.com/4515176