> But the set of specific types is "int".
But the *type set* is "int"...
On Thursday, January 6, 2022 at 11:57:59 AM UTC-5 Jason Phillips wrote:
> 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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