code review 5498053: effective_go: redeclaration

effective_go: redeclaration

Fixes issue 2455.
Fixes issue 2013.

[r, 2011-12-20 21:37:37]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go

[r, 2011-12-20 21:40:52]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com),

Please take another look.

[rsc, 2011-12-20 21:41:41]

I feel like many people will think that

x := 1
{
    x := 2
}

is an example of redeclaration.  It would be very nice
to use a different word for the not-declaration of x in

x := 1
x, y := 2, 3

but I don't have a better word handy.

http://codereview.appspot.com/5498053/diff/1/doc/effective_go.html
File doc/effective_go.html (left):

http://codereview.appspot.com/5498053/diff/1/doc/effective_go.html#oldcode503
doc/effective_go.html:503: <p id="else">
Please restore id tag so that links to
http://golang.org/doc/effective_go.html#else
continue to work.

[r2, 2011-12-20 21:44:34]

On Dec 20, 2011, at 1:41 PM, rsc@golang.org wrote:

> I feel like many people will think that
> 
> x := 1
> {
>    x := 2
> }
> 
> is an example of redeclaration.  It would be very nice
> to use a different word for the not-declaration of x in
> 
> x := 1
> x, y := 2, 3
> 
> but I don't have a better word handy.

that's why it says 'in the same scope'.

programmers don't understand scope but i don't know how to address that here.

-rob

[r, 2011-12-20 21:44:40]

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

Please take another look.

[rsc, 2011-12-20 21:48:24]

http://codereview.appspot.com/5498053/diff/7001/doc/effective_go.html
File doc/effective_go.html (right):

http://codereview.appspot.com/5498053/diff/7001/doc/effective_go.html#newcode572
doc/effective_go.html:572: In a <code>:=</code> declaration it is legal to
redeclare a variable as long as it is
I think the main thing that bothers me is the "it is legal",
because there are other legal uses of := that do not 
redeclare the variable (in this sense).  Maybe something
that describes the effect instead of describing legality?

In a <code>:=</code> declaration, a variable on the left hand side is treated
as redeclared if it has already been declared in the current scope.
A <code>:=</code> declaration must include at least one new variable
on its left hand side.

[gri, 2011-12-20 21:54:33]

On Tue, Dec 20, 2011 at 1:48 PM,  <rsc@golang.org> wrote:
> In a <code>:=</code> declaration, a variable on the left hand side is
> treated
> as redeclared if it has already been declared in the current scope.
> A <code>:=</code> declaration must include at least one new variable
> on its left hand side.

Or perhaps (since it's not a redeclaration):

In a <code>:=</code> declaration, a variable on the left hand side may
be referred to (mentioned?)
without redeclaration error if it has already been declared in the
current scope.
A <code>:=</code> declaration must include at least one new variable
on its left hand side.

Otherwise, LGTM.
- gri

[r, 2011-12-20 21:57:03]

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

Please take another look.

[r2, 2011-12-20 21:57:06]

On Dec 20, 2011, at 1:48 PM, rsc@golang.org wrote:

> 
> http://codereview.appspot.com/5498053/diff/7001/doc/effective_go.html
> File doc/effective_go.html (right):
> 
>
http://codereview.appspot.com/5498053/diff/7001/doc/effective_go.html#newcode572
> doc/effective_go.html:572: In a <code>:=</code> declaration it is legal
> to redeclare a variable as long as it is
> I think the main thing that bothers me is the "it is legal",
> because there are other legal uses of := that do not
> redeclare the variable (in this sense).  Maybe something
> that describes the effect instead of describing legality?
> 
> In a <code>:=</code> declaration, a variable on the left hand side is
> treated
> as redeclared if it has already been declared in the current scope.
> A <code>:=</code> declaration must include at least one new variable
> on its left hand side.
> 
> http://codereview.appspot.com/5498053/

"treated as redeclared" seems to me to be far more confusing than what i had.

PTAL.


-rob

[gri, 2011-12-20 21:59:57]

LGTM

http://codereview.appspot.com/5498053/diff/3005/doc/effective_go.html
File doc/effective_go.html (right):

http://codereview.appspot.com/5498053/diff/3005/doc/effective_go.html#newcode572
doc/effective_go.html:572: In a <code>:=</code> declaration a variable
<code>v</code> may appear even
may appear on the left-hand side (?)

[r, 2011-12-20 22:00:21]

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

Please take another look.

[rsc, 2011-12-20 22:08:37]

LGTM

http://codereview.appspot.com/5498053/diff/4008/doc/effective_go.html
File doc/effective_go.html (right):

http://codereview.appspot.com/5498053/diff/4008/doc/effective_go.html#newcode578
doc/effective_go.html:578: (if <code>v</code> is declared in an outer scope, a
new declaration will create a new variable),</li>
s/a new/the/

http://codereview.appspot.com/5498053/diff/4008/doc/effective_go.html#newcode580
doc/effective_go.html:580: <li>there is at least one variable in the declaration
that is being declared anew.</li>
s/one/& other/

[r, 2011-12-20 22:15:38]

*** Submitted as 6bd78dcec1cd ***

effective_go: redeclaration

Fixes issue 2455.
Fixes issue 2013.

R=rsc, r, gri
CC=golang-dev
http://codereview.appspot.com/5498053

http://codereview.appspot.com/5498053/diff/1/doc/effective_go.html
File doc/effective_go.html (left):

http://codereview.appspot.com/5498053/diff/1/doc/effective_go.html#oldcode503
doc/effective_go.html:503: <p id="else">
it seemed wrong to me, but i see now.
Done.