code review 5672078: faq: add entry about nil interfaces vs. nil pointers

faq: add entry about nil interfaces vs. nil pointers

Fixes issue 2778.

[r, 2012-02-17 04:31:03]

Hello golang-dev@googlegroups.com,

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

[bradfitz, 2012-02-17 04:38:59]

http://codereview.appspot.com/5672078/diff/1/doc/go_faq.html
File doc/go_faq.html (right):

http://codereview.appspot.com/5672078/diff/1/doc/go_faq.html#newcode729
doc/go_faq.html:729: var p *MyError = nil
p defined but not used

[rsc1, 2012-02-17 04:45:15]

It might be worth saying that as a consequence,
a good rule of thumb is that functions that return
errors should always return them as interfaces,
not as concrete types.  This is why, for example,
os.Open returns error even though the underlying
type is, we promise, an *os.PathError.

http://codereview.appspot.com/5672078/diff/1/doc/go_faq.html
File doc/go_faq.html (right):

http://codereview.appspot.com/5672078/diff/1/doc/go_faq.html#newcode688
doc/go_faq.html:688: Under the covers, interfaces are implemented by two
elements, a value and a type.
s/by/as/

http://codereview.appspot.com/5672078/diff/1/doc/go_faq.html#newcode691
doc/go_faq.html:691: schematically, (<code>3</code>, <code>int</code>).
Maybe swap these?  (int, 3) puts first the information you need
to interpret the second half.  Also the type is the key part here.

http://codereview.appspot.com/5672078/diff/1/doc/go_faq.html#newcode712
doc/go_faq.html:712: p == ErrBad
s/==/=/

[r, 2012-02-17 05:04:07]

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

Please take another look.

[iant, 2012-02-17 05:11:46]

LGTM

http://codereview.appspot.com/5672078/diff/5001/doc/go_faq.html
File doc/go_faq.html (right):

http://codereview.appspot.com/5672078/diff/5001/doc/go_faq.html#newcode688
doc/go_faq.html:688: Under the covers, interfaces are implemented as two
elements, a type and a value.
The spec calls this the "dynamic type;" perhaps we could work that in here
somewhere.

http://codereview.appspot.com/5672078/diff/5001/doc/go_faq.html#newcode719
doc/go_faq.html:719: When the function returns <code>p</code>, the return value
is an <code>error</code> interface
Perhaps "When the function succeeds and returns...."  Otherwise the text
suggests that the function always returns p == nil.

http://codereview.appspot.com/5672078/diff/5001/doc/go_faq.html#newcode730
doc/go_faq.html:730: var p *MyError = nil
No need for the variable p in this example.

[adg, 2012-02-17 05:19:07]

http://codereview.appspot.com/5672078/diff/5001/doc/go_faq.html
File doc/go_faq.html (right):

http://codereview.appspot.com/5672078/diff/5001/doc/go_faq.html#newcode695
doc/go_faq.html:695: An interface value is <code>nil</code> only if the inner
value and type are both unset.
s/\./, (nil, nil)./

And I think you could make better use of the "schematic" form in this paragraph.

[r, 2012-02-17 05:20:38]

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

Please take another look.

[rsc1, 2012-02-17 05:21:40]

LGTM

http://codereview.appspot.com/5672078/diff/5001/doc/go_faq.html
File doc/go_faq.html (right):

http://codereview.appspot.com/5672078/diff/5001/doc/go_faq.html#newcode730
doc/go_faq.html:730: var p *MyError = nil
On 2012/02/17 05:11:46, iant wrote:
> No need for the variable p in this example.

Agree; delete.

[r, 2012-02-17 05:22:14]

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

Please take another look.

[rsc1, 2012-02-17 05:23:26]

LGTM

[adg, 2012-02-17 05:24:19]

http://codereview.appspot.com/5672078/diff/3004/doc/go_faq.html
File doc/go_faq.html (right):

http://codereview.appspot.com/5672078/diff/3004/doc/go_faq.html#newcode701
doc/go_faq.html:701: (<code>*int</code>, <code>nil</code>)
missing a period here

[r, 2012-02-17 05:27:22]

*** Submitted as 51793ab42fa9 ***

faq: add entry about nil interfaces vs. nil pointers

Fixes issue 2778.

R=bradfitz, rsc, iant, adg
CC=golang-dev
http://codereview.appspot.com/5672078