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cmd/compile: unsafe.Pointer not treated as a pointer for embedding #6357

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griesemer opened this issue Sep 10, 2013 · 6 comments
Closed

cmd/compile: unsafe.Pointer not treated as a pointer for embedding #6357

griesemer opened this issue Sep 10, 2013 · 6 comments
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@griesemer
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http://play.golang.org/p/YhdG1ZoVzp

Per the spec: "An embedded type must be specified as a type name T or as a pointer
to a non-interface type name *T, and T itself may not be a pointer type."  (
http://tip.golang.org/ref/spec#Struct_types )

gc issues an error for line 9 (as expected), but not for line 10. Arguably, an
unsafe.Pointer is a pointer and thus line 10 should not be legal.

The spec is not very clear about whether an unsafe.Pointer should act like a pointer in
these situations, but:

1. The documentation (by pseudo code) defines unsafe.Pointer as *ArbitraryType (
http://tip.golang.org/ref/spec#Package_unsafe )

2. For the purposes of method receivers, they are treated as pointers (see issue #6116)

3. It's ok to assign nil to it (see line 15 of the above code).

4. It's called a "Pointer".
@griesemer
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Comment 1:

PS: gccgo reports an error for line 9 and 10:
x.go:9:6: error: embedded type may not be a pointer
      P1
      ^
x.go:10:6: error: embedded type may not be a pointer
      P2
      ^

@rsc
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rsc commented Nov 27, 2013

Comment 2:

Labels changed: added go1.3maybe.

@rsc
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rsc commented Dec 4, 2013

Comment 3:

Labels changed: added release-none, removed go1.3maybe.

@rsc
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rsc commented Dec 4, 2013

Comment 4:

Labels changed: added repo-main.

@rsc rsc removed the compiler-bug label Apr 10, 2015
@rsc rsc added this to the Unplanned milestone Apr 10, 2015
@rsc rsc changed the title cmd/gc: unsafe.Pointer not treated as a pointer for embedding cmd/compile: unsafe.Pointer not treated as a pointer for embedding Jun 8, 2015
@akovaski akovaski mentioned this issue Dec 26, 2015
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tycho added a commit to tycho/go-sdl2 that referenced this issue Dec 26, 2015
@tycho
sdl_mixer: fix compile error with gccgo
416a73b 
With gccgo I was getting this:

    $ go build
    # github.com/veandco/go-sdl2/sdl_mixer
    ./sdl_mixer.go:83:2: error: embedded type may not be a pointer
      unsafe.Pointer
      ^

Apparently upstream Go hasn't yet added the above error[1].

Fixes veandco#167.

[1] golang/go#6357

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
@tycho tycho mentioned this issue Dec 26, 2015
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@odeke-em
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odeke-em commented Jun 6, 2020

Good news @griesemer, this issue has been fixed since at least Go1.7 (I couldn't get Go1.6 and earlier to build on my Macbook Pro) and it rightly matches gccgo's behavior producing

Go1.7

$ go version && go run main.go 
go version go1.7.6 darwin/amd64
# command-line-arguments
./main.go:9: embedded type cannot be a pointer
./main.go:10: embedded type cannot be a pointer

Go1.8

 go version && go run main.go 
go version go1.8.7 darwin/amd64
# command-line-arguments
./main.go:9: embedded type cannot be a pointer
./main.go:10: embedded type cannot be a pointer

Go1.9

$ go version && go run main.go 
go version go1.9.7 darwin/amd64
# command-line-arguments
./main.go:9:2: embedded type cannot be a pointer
./main.go:10:2: embedded type cannot be a pointer

Go1.10

$ go version && go run main.go 
go version go1.10.8 darwin/amd64
# command-line-arguments
./main.go:9:2: embedded type cannot be a pointer
./main.go:10:2: embedded type cannot be a pointer

Go1.11

$ go version && go run main.go 
go version go1.11.13 darwin/amd64
# command-line-arguments
./main.go:9:2: embedded type cannot be a pointer
./main.go:10:2: embedded type cannot be a pointer

Go1.12

$ go version && go run main.go 
go version go1.12.16 darwin/amd64
# command-line-arguments
./main.go:9:2: embedded type cannot be a pointer
./main.go:10:2: embedded type cannot be a pointer

Go1.13

$ go version && go run main.go 
go version go1.13.11 darwin/amd64
# command-line-arguments
./main.go:9:2: embedded type cannot be a pointer
./main.go:10:2: embedded type cannot be a pointer

Go1.14

$ go version && go run main.go 
go version go1.14.3 darwin/amd64
# command-line-arguments
./main.go:9:2: embedded type cannot be a pointer
./main.go:10:2: embedded type cannot be a pointer

I shall let you close this issue as you please. Thank you.

@griesemer
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Appears fixed per the above comment. Verified in latest playground. Closing.

@golang golang locked and limited conversation to collaborators Aug 12, 2021
@rsc rsc removed their assignment Jun 22, 2022
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