And by "first paragraph of the spec" I mean "first paragraph of the
Structure of interfaces section of the spec". Apologies.
On Thursday, January 6, 2022 at 11:11:45 AM UTC-5 Jason Phillips wrote:
> @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?
>>>>>>
>>>>>
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