code review 101500044: spec: receiver declaration is just a parameter declaration

spec: receiver declaration is just a parameter declaration

This CL removes the special syntax for method receivers and
makes it just like other parameters. Instead, the crucial
receiver-specific rules (exactly one receiver, receiver type
must be of the form T or *T) are specified verbally instead
of syntactically.

This is a fully backward-compatible (and minor) syntax
relaxation. As a result, the following syntactic restrictions
(which are completely irrelevant) and which were only in place
for receivers are removed:

a) receiver types cannot be parenthesized
b) receiver parameter lists cannot have a trailing comma

The result of this CL is a simplication of the spec and the
implementation, with no impact on existing (or future) code.

Noteworthy:

- gc already permits a trailing comma at the end of a receiver
  declaration:

  func (recv T,) m() {}

  This is technically a bug with the current spec; this CL will
  legalize this notation.

- gccgo produces a misleading error when a trailing comma is used:

  error: method has multiple receivers

  (even though there's only one receiver)

- Compilers and type-checkers won't need to report errors anymore
  if receiver types are parenthesized.

Fixes issue 4496.

[gri, 2014-06-24 19:59:28]

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

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

[iant, 2014-06-24 20:28:37]

LGTM

Note that this requires changing test/fixedbugs/bug299.go.

[gri, 2014-06-24 20:36:24]

On Tue, Jun 24, 2014 at 1:28 PM, <iant@golang.org> wrote:

> LGTM
>
> Note that this requires changing test/fixedbugs/bug299.go.
>

Will need to change that once the compilers are adjusted.

[rsc, 2014-06-24 20:39:02]

LGTM

[rsc, 2014-06-24 20:40:28]

FWIW I think gc implements not just trailing comma but also the parsing of
(x T, y T) as an (invalid) receiver.
So the only gc change here is to stop caring about parenthesization.

[gri, 2014-06-24 20:42:13]

Makes sense. The go/parser does the same. Overall this will just bring the
spec more in line with the way implementations are done anyway.
- gri


On Tue, Jun 24, 2014 at 1:40 PM, Russ Cox <rsc@golang.org> wrote:

> FWIW I think gc implements not just trailing comma but also the parsing of
> (x T, y T) as an (invalid) receiver.
> So the only gc change here is to stop caring about parenthesization.
>
>

[rsc, 2014-06-24 20:47:22]

CL 110160044 implements this in cmd/gc and fixes test/fixedbugs/bug299.

[rsc, 2014-06-24 20:47:23]

CL 110160044 implements this in cmd/gc and fixes test/fixedbugs/bug299.

[gri, 2014-06-24 23:25:13]

*** Submitted as https://code.google.com/p/go/source/detail?r=fbd4c26ecc93 ***

spec: receiver declaration is just a parameter declaration

This CL removes the special syntax for method receivers and
makes it just like other parameters. Instead, the crucial
receiver-specific rules (exactly one receiver, receiver type
must be of the form T or *T) are specified verbally instead
of syntactically.

This is a fully backward-compatible (and minor) syntax
relaxation. As a result, the following syntactic restrictions
(which are completely irrelevant) and which were only in place
for receivers are removed:

a) receiver types cannot be parenthesized
b) receiver parameter lists cannot have a trailing comma

The result of this CL is a simplication of the spec and the
implementation, with no impact on existing (or future) code.

Noteworthy:

- gc already permits a trailing comma at the end of a receiver
  declaration:

  func (recv T,) m() {}

  This is technically a bug with the current spec; this CL will
  legalize this notation.

- gccgo produces a misleading error when a trailing comma is used:

  error: method has multiple receivers

  (even though there's only one receiver)

- Compilers and type-checkers won't need to report errors anymore
  if receiver types are parenthesized.

Fixes issue 4496.

LGTM=iant, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://codereview.appspot.com/101500044