@Brian
> interface{ int; m() } // *[specific type]* int (but type set is empty
because int has no method m)
> interface{ int; any } // no specific types (intersection is empty) *[even
though the type set is not empty]*
As noted in the first paragraph of the spec, the set of specific types is
calculated by only considering type elements in the interface. Given that,
I think the spec note is wrong in the example being discussed. It should be
"int". Also, regardless of the answer, surely the specific types for
"interface{ int; m() }" and "interface{ int; any}" are always the same?
On Thursday, January 6, 2022 at 10:37:55 AM UTC-5 tapi...@gmail.com wrote:
> On Thursday, January 6, 2022 at 11:19:40 PM UTC+8 tapi...@gmail.com wrote:
>
>> On Thursday, January 6, 2022 at 9:40:52 PM UTC+8 tapi...@gmail.com wrote:
>>
>>> On Thursday, January 6, 2022 at 8:35:06 PM UTC+8 Brian Candler wrote:
>>>
>>>> No, the mistake is in your reading of the spec. You are complaining
>>>> about this line:
>>>>
>>>> interface{ int; any } // no specific types (intersection is empty)
>>>>
>>>> The spec makes it clear that:
>>>> 1. "any" is short for "interface {}"
>>>> 2. "interface {}" has no *specific types*
>>>>
>>>>
>>> I think your logic mistake here is that the operands of the union and
>>> intersection operations are type sets, instead of specific types.
>>>
>>
>> This conclusion is not very precise. More precisely, the operands of the
>> union and intersection operations
>> could be either type set or specific types, but interface types don't
>> participate in calculations of specific types.
>>
>
> This is still not precise. More precisely speaking, in calculations of
> specific types,
> interface types don't participate in intersection operations,
> and only "any" (interface{}) is allowed to participate in union operations.
> The result of a union operation with any as an operand is a blank set.
>
>
>>
>>
>>>
>>>
>>>> You are taking the intersection of the set of one type (int) with the
>>>> empty set, and therefore the result is the empty set. Exactly as the
>>>> comment says.
>>>>
>>>> On Thursday, 6 January 2022 at 11:47:52 UTC tapi...@gmail.com wrote:
>>>>
>>>>> On Thursday, January 6, 2022 at 6:15:06 PM UTC+8 Brian Candler wrote:
>>>>>
>>>>>> 1. interface { a;b } is intersection. The "Intersection" between two
>>>>>> sets means things which exist in both sets simultaneously.
>>>>>> 2. interface { a|b } is union. "Union" means a set of things which
>>>>>> which exist in set A *or* set B.
>>>>>>
>>>>>> Quoting from the spec:
>>>>>> *"the predeclared type *any* is an alias for the empty interface." *
>>>>>> *"interface{} // no specific types"*
>>>>>> *"For an interface with type elements, 𝑆 is the intersection of the
>>>>>> specific types of its type elements."*
>>>>>>
>>>>>> Can you see now?
>>>>>>
>>>>>
>>>>> The explanation is as what I think.
>>>>> But what is your conclusion? Is it a mistake in spec?
>>>>>
>>>>
--
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/bd5b6350-dbbf-4468-b648-f4b497c856ccn%40googlegroups.com.
