Re: [go-nuts] Ambiguous Method Promotion Bug?

['Axel Wagner' via golang-nuts]

"and so does zz.X.Fun", of course.

On Tue, Nov 17, 2020 at 10:14 PM Axel Wagner 
wrote:

> Hi,
>
> the relevant spec section is https://golang.org/ref/spec#Selectors
>
> A selector f may denote a field or method f of a type T, or it may refer
>> to a field or method f of a nested embedded field of T. The number of
>> embedded fields traversed to reach f is called its depth in T. The depth of
>> a field or method f declared in T is zero. The depth of a field or method f
>> declared in an embedded field A in T is the depth of f in A plus one.
>
>
> and
>
> For a value x of type T or *T where T is not a pointer or interface type,
>> x.f denotes the field or method at the shallowest depth in T where there is
>> such an f. If there is not exactly one f with shallowest depth, the
>> selector expression is illegal.
>
>
> In your example, zz.Fun refers to zz.Y.Fun, as that has a depth of 1,
> whereas zz.Q.Fun has a depth of 2 (Q has depth 1 and Fun has depth 1 within
> Q) and zz.X.Fun (X has depth 2 in Z and Fun has depth 0 in X).
>
> Note, in particular, that the check happens at the selector expression,
> not at the type-definition. This is intentional, as it means you can embed
> multiple types without it being an error if they have the same
> fields/methods.
>
> I agree that all of this makes not necessarily for the most readable code,
> but the rule that the shallowest depth must be unique is what makes the
> selector well-defined.
>
> On Tue, Nov 17, 2020 at 9:57 PM Michal Ostrowski 
> wrote:
>
>>
>> Here is a playground doc that demonstrates what seems to be strange
>> behavior regarding promotion of methods.
>>
>> https://play.golang.org/p/R9M1lAOd9CA
>>
>> It seems that I can generate a struct a have an ambiguous method by
>> adding a level of indirection in struct definitions.  Or there's something
>> in the language spec that I'm missing (and I'd appreciate a reference to
>> that in that case.)
>>
>>
>>
>> --
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>> 
>> .
>>
>

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Re: [go-nuts] Ambiguous Method Promotion Bug?

['Axel Wagner' via golang-nuts]

Hi,

the relevant spec section is https://golang.org/ref/spec#Selectors

A selector f may denote a field or method f of a type T, or it may refer to
> a field or method f of a nested embedded field of T. The number of embedded
> fields traversed to reach f is called its depth in T. The depth of a field
> or method f declared in T is zero. The depth of a field or method f
> declared in an embedded field A in T is the depth of f in A plus one.


and

For a value x of type T or *T where T is not a pointer or interface type,
> x.f denotes the field or method at the shallowest depth in T where there is
> such an f. If there is not exactly one f with shallowest depth, the
> selector expression is illegal.


In your example, zz.Fun refers to zz.Y.Fun, as that has a depth of 1,
whereas zz.Q.Fun has a depth of 2 (Q has depth 1 and Fun has depth 1 within
Q) and zz.X.Fun (X has depth 2 in Z and Fun has depth 0 in X).

Note, in particular, that the check happens at the selector expression, not
at the type-definition. This is intentional, as it means you can embed
multiple types without it being an error if they have the same
fields/methods.

I agree that all of this makes not necessarily for the most readable code,
but the rule that the shallowest depth must be unique is what makes the
selector well-defined.

On Tue, Nov 17, 2020 at 9:57 PM Michal Ostrowski  wrote:

>
> Here is a playground doc that demonstrates what seems to be strange
> behavior regarding promotion of methods.
>
> https://play.golang.org/p/R9M1lAOd9CA
>
> It seems that I can generate a struct a have an ambiguous method by adding
> a level of indirection in struct definitions.  Or there's something in the
> language spec that I'm missing (and I'd appreciate a reference to that in
> that case.)
>
>
>
> --
> You received this message because you are subscribed to the Google Groups
> "golang-nuts" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to golang-nuts+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/golang-nuts/cb606644-1b76-4db1-af8c-96b5efac1c20n%40googlegroups.com
> 
> .
>

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[go-nuts] Ambiguous Method Promotion Bug?

[Michal Ostrowski]

Here is a playground doc that demonstrates what seems to be strange 
behavior regarding promotion of methods.

https://play.golang.org/p/R9M1lAOd9CA

It seems that I can generate a struct a have an ambiguous method by adding 
a level of indirection in struct definitions.  Or there's something in the 
language spec that I'm missing (and I'd appreciate a reference to that in 
that case.)



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