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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