On Mon, Feb 5, 2018 at 10:42 AM, theckman via golang-nuts
<golang-nuts@googlegroups.com> wrote:
> Hey Gophers,
>
> I've run in to an interesting case regarding Method Sets that makes me
> wonder whether it should be disallowed by the spec[1]. Before opening an
> issue on GitHub I thought I'd reach out here to get some clarifications as I
> may be misreading the spec.
>
> Based on my understanding of method sets, a variable with the type *T should
> have a method set that contains methods on T and *T, while a variable of
> type T should only have methods with a receiver for T in the method set. To
> me this translates that if my variable is not a pointer type it should not
> be able to call a method that's receiving a pointer type.
I believe this is not what the spec says. If type T has:
func (t T) A() {}
func (t *T) B() {}
Then the method set of T is [A], where the method set of *T is [A,B]
For a variable x:=T{}, x.A() is called with a copy of x, and x.B() is
called with a copy of &x. So, for instance:
func f(m map[string]T) {
m["key"].A() // works
m["key"].B() // doesn't work, m["key"] is not addressable
>
> However, I've observed that to not be the case. If I have a variable of type
> T, I am able to invoke methods that are receiving *T[2]. Should that be
> permitted by the spec? It adds some inconsistency because I am able to
> invoke the method on my variable, but the variable won't satisfy an
> interface that has that method included[3]. I think it's acceptable that the
> interface isn't satisfied, but what makes it so that invoking the method
> directly is permitted?
>
> Cheers!
> -Tim
>
> [1] https://golang.org/ref/spec#Method_sets
> [2] https://play.golang.org/p/-OMAnD7U0Vl
> [3] https://play.golang.org/p/uP0_eMYqYEe
>
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