code review 95560046: reflect: don't panic on delete from nil map.

reflect: don't panic on delete from nil map.

Fixes issue 8051

[khr, 2014-05-20 21:12:40]

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

I'd like you to review this change to
https://khr%40golang.org@code.google.com/p/go/

[bradfitz, 2014-05-20 21:17:04]

LGTM

I never knew that SetMapIndex with a zero value was defined as delete.
Reminds of of m[k] = 0, false.



On Tue, May 20, 2014 at 2:12 PM, <khr@golang.org> wrote:

> Reviewers: golang-codereviews,
>
> Message:
> Hello golang-codereviews@googlegroups.com (cc:
> golang-codereviews@googlegroups.com),
>
> I'd like you to review this change to
> https://khr%40golang.org@code.google.com/p/go/
>
>
> Description:
> reflect: don't panic on delete from nil map.
>
> Please review this at https://codereview.appspot.com/95560046/
>
> Affected files (+4, -1 lines):
>   M src/pkg/reflect/all_test.go
>   M src/pkg/runtime/hashmap.goc
>
>
> Index: src/pkg/reflect/all_test.go
> ===================================================================
> --- a/src/pkg/reflect/all_test.go
> +++ b/src/pkg/reflect/all_test.go
> @@ -993,6 +993,9 @@
>         if x.Kind() != Invalid {
>                 t.Errorf("mbig.MapIndex(\"hello\") for nil map = %v, want
> Invalid Value", x)
>         }
> +
> +       // Test that deletes from a nil map succeed.
> +       mv.SetMapIndex(ValueOf("hi"), Value{})
>  }
>
>  func TestChan(t *testing.T) {
> Index: src/pkg/runtime/hashmap.goc
> ===================================================================
> --- a/src/pkg/runtime/hashmap.goc
> +++ b/src/pkg/runtime/hashmap.goc
> @@ -990,7 +990,7 @@
>  #pragma textflag NOSPLIT
>  func reflect·mapdelete(t *MapType, h *Hmap, key *byte) {
>         if(h == nil)
> -               runtime·panicstring("delete from nil map");
> +               return; // see bug 8051
>         if(raceenabled) {
>                 runtime·racewritepc(h, runtime·getcallerpc(&t),
> reflect·mapdelete);
>                 runtime·racereadobjectpc(key, t->key,
> runtime·getcallerpc(&t), reflect·mapdelete);
>
>
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[khr, 2014-05-20 23:26:07]

*** Submitted as https://code.google.com/p/go/source/detail?r=cd23c6e8c798 ***

reflect: don't panic on delete from nil map.

Fixes issue 8051

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/95560046