I take my argument back, I agree with Brian here. According to the spec
"interface{}" is a type element because it contains no methods. So the
intersection of the specific types "interface{}" and "int" is an empty set.
But the set of specific types is "int".
On Thursday, January 6, 2022 at 11:34:02 AM UTC-5 Jason Phillips wrote:
> 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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