reflect: Value's == behavior changed between 1.3 and 1.4

[hsinhoyeh]

the following code snippet has different behavior when I run it on 1.3 and 1.4 respectively.
code are in https://play.golang.org/p/yfy7ZKqU1Y

when I run on 1.3, we have the following response:

false
0
0x0
true

while, It report false in the last println in golang 1.4

false
0
0x0
false

not sure whether it is a bug or something

[bradfitz]

I don't think you should use == on a reflect.Value. Perhaps that just needs to be documented.

/cc @robpike, @randall77

[hsinhoyeh]

ok, then how to test the equality of reflect.Value instead of using "=="?
any suggestion?

[minux]

It's not a bug.

You shouldn't use == to compare two reflect.Value for equality.

The reason it's different is that starting from Go 1.4, interface values
will always store a pointer, so is reflect.Value. Thus, although the two
reflect.Value's are indeed storing the same integer, the struct itself
are not equal (the ptr field are different)

[adg]

I think v1.Interface() == v2.Interface() will probably do what you want.

[minux]

And even on Go 1.3, types that can't be stored into interfaces inline will
exhibit the similar behavior (two reflect.Value's representing two equal
values are not equal).

https://play.golang.org/p/Dhe5Qm_vtH

[hsinhoyeh]

@minux you are right.
golang 1.4 always stores interface values into a pointer
https://github.com/golang/go/blob/release-branch.go1.4/src/reflect/value.go#L138
, whereas golang 1.3 does the separated things.

@adg thanks, Interface() can test this.