Two values A and B are equal (A==B) if A and B have the same type and the
same values. In a code where
a:=clientContextKey{}
b:=clientContextKey{}
a==b is true, because they have the same types, and they have the same
values (i.e. the empty value).
Note however:
a:=&clientContextKey{}
b:=&clientContextKey{}
It is not guaranteed that a==b, neither is it guaranteed that a!=b. The
compiler may choose to allocate the same address for the zero-size
variables a and b, or it may not,
On Sun, May 28, 2023 at 7:01 AM cpu...@gmail.com <cpui...@gmail.com> wrote:
> I've recently stumbled across code like this
> https://go.dev/play/p/u3UER2ywRlr:
>
> type clientContextKey struct{}
>
> ctx := context.Background()
> ctx = context.WithValue(ctx, clientContextKey{}, "foo")
> _, ok := ctx.Value(clientContextKey{}).(string)
>
> Naively, I had expected this to fail since I assumed that
> clientContextKey{} would create a new variable instance every time it was
> used and hence the keys would not match.
>
> Why does this use of instantiating the struct type work here?
>
> Thanks,
> Andi
>
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