code review 6680044: cmd/go: add join template function.

cmd/go: add join template function.

It's common to use the go list command in shell scripts, but
currently it's awkward to print a string slice from the Package
type in a way that's easily parseable by the shell.  For example:

        go list -f '{{range .Deps}}{{.}}
        {{end}}'

(and even that prints an unwanted new line at the end|).

To make this easier, this CL adds a "join" function to the
format template.

        go list -f '{{join .Deps "\n"}}'

[rog, 2012-10-13 12:11:50]

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

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

[dsymonds, 2012-10-13 12:23:38]

A join function would be better.

[minux1, 2012-10-13 12:27:00]

https://codereview.appspot.com/6680044/diff/5001/src/cmd/go/list.go
File src/cmd/go/list.go (right):

https://codereview.appspot.com/6680044/diff/5001/src/cmd/go/list.go#newcode130
src/cmd/go/list.go:130: if out.Count() > 0 {
i still prefer to fix the extra \n problem at least.
(I don't oppose to the added list function)

i think the reason why cmd/go will add a \n unconditionally
is to avoid miss one at the end,
but the logic here can be changed to provide extra \n
only when really necessary.

https://codereview.appspot.com/6680044/diff/5001/src/cmd/go/list.go#newcode159
src/cmd/go/list.go:159: func (cw *CountingWriter) Write(p []byte) (n int, err
error) {
for example, we only need to look at p[len(p)-1],
and if it is '\n' set count = 0; otherwise set count=1;
no other code need to be changed to remove the
extra \n.

(if we choose to go this route, CountingWriter should be
renamed)

[remyoudompheng, 2012-10-13 12:34:31]

I also prefer join. Especially if I can write {{ .Deps | join ", " }}

2012/10/13, David Symonds <dsymonds@golang.org>:
> A join function would be better.
>

[minux1, 2012-10-13 12:38:48]

On Sat, Oct 13, 2012 at 8:34 PM, Rémy Oudompheng
<remyoudompheng@gmail.com>wrote:

> I also prefer join. Especially if I can write {{ .Deps | join ", " }}
>
+1. join without hardcoding join character to \n is more useful.

[rog, 2012-10-15 09:48:57]

Hello rsc@golang.org, dsymonds@golang.org, minux.ma@gmail.com,
remyoudompheng@gmail.com (cc: golang-dev@googlegroups.com),

Please take another look.

[rsc, 2012-10-16 17:36:14]

I like the idea. Not sure it makes sense to swap the arguments. Now you can do

{{join .Deps ","}}

and even

{{join (complex|pipeline) ","}

I understand the rationale for putting it first, but it makes it different from
strings.Join, which I think will confuse Go programmers.

[rog, 2012-10-17 15:05:00]

Hello rsc@golang.org, dsymonds@golang.org, minux.ma@gmail.com,
remyoudompheng@gmail.com (cc: golang-dev@googlegroups.com),

Please take another look.

[dsymonds, 2012-10-17 22:41:29]

LGTM

http://codereview.appspot.com/6680044/diff/20002/src/cmd/go/list.go
File src/cmd/go/list.go (right):

http://codereview.appspot.com/6680044/diff/20002/src/cmd/go/list.go#newcode31
src/cmd/go/list.go:31: which takes a slice of strings and a separator string and
returns
maybe it'd be simpler to reference strings.Join here, and then the user has a
place to go to read about edge cases.

[rog, 2012-10-18 10:01:51]

http://codereview.appspot.com/6680044/diff/20002/src/cmd/go/list.go
File src/cmd/go/list.go (right):

http://codereview.appspot.com/6680044/diff/20002/src/cmd/go/list.go#newcode31
src/cmd/go/list.go:31: which takes a slice of strings and a separator string and
returns
On 2012/10/17 22:41:29, dsymonds wrote:
> maybe it'd be simpler to reference strings.Join here, and then the user has a
> place to go to read about edge cases.

I considered this, but there really aren't any edge cases, and in general I
think it's nicer if docs for a command don't require looking in the package docs
too.

However, maybe:

// One extra template function is available, "join"
// which calls strings.Join.

is less awkward, and everyone should know about strings.Join already, right?

I'll go with that unless you or others have a better suggestion.

[r, 2012-10-18 10:55:41]

This all feels too ad hoc to me.

-rob

[rog, 2012-10-18 12:05:34]

Yes, it is ad hoc. I'd really like to be able to conveniently use go list
in shell scripts though. If you wanted to suggest adding
something that granted similar convenience to all templates,
I'd be very happy.

On 18 October 2012 11:55, Rob Pike <r@golang.org> wrote:
> This all feels too ad hoc to me.
>
> -rob

[r, 2012-10-19 21:24:18]

After cogitation and discussion I'm OK with this.

http://codereview.appspot.com/6680044/diff/20002/src/cmd/go/list.go
File src/cmd/go/list.go (right):

http://codereview.appspot.com/6680044/diff/20002/src/cmd/go/list.go#newcode31
src/cmd/go/list.go:31: which takes a slice of strings and a separator string and
returns
For people using this feature of cmd/go, some programming ability is expected. I
think your rewrite is good, except for the missing comma after "join".

[rog, 2012-10-22 07:59:07]

*** Submitted as http://code.google.com/p/go/source/detail?r=117f773ed6b0 ***

cmd/go: add join template function.

It's common to use the go list command in shell scripts, but
currently it's awkward to print a string slice from the Package
type in a way that's easily parseable by the shell.  For example:

        go list -f '{{range .Deps}}{{.}}
        {{end}}'

(and even that prints an unwanted new line at the end|).

To make this easier, this CL adds a "join" function to the
format template.

        go list -f '{{join .Deps "\n"}}'

R=rsc, dsymonds, minux.ma, remyoudompheng, r
CC=golang-dev
http://codereview.appspot.com/6680044