On Saturday, December 10, 2016 at 4:11:43 PM UTC+8, Axel Wagner wrote:
>
> On Sat, Dec 10, 2016 at 9:00 AM, T L <tapi...@gmail.com <javascript:>>
> wrote:
>
>>
>>
>> On Saturday, December 10, 2016 at 3:42:34 PM UTC+8, Axel Wagner wrote:
>>>
>>> I don't understand. You are saying, that you want a method on a pointer
>>> to Age and then find it unreasonable, that you are getting a method on a
>>> pointer to Age?
>>>
>>> If you don't want the argument to be a pointer, use Age.CanDrink
>>> instead. Both are valid, because the method set of *Age contains all
>>> methods declared on *Age or on Age (according to the spec
>>> <https://golang.org/ref/spec#Method_sets>).
>>>
>>
>> That is what it is weird, Age.CanDrink and (*Age).CanDrink should be the
>> same function.
>>
>
> Why? Age and *Age are different types. Why would they be interchangeable
> in this case? When the programmer *explicitly* asked for different
> things? That seems like confusing (and infuriating) behavior to me.
> You need to come up with a reason why this should be the case, you can't
> simply state that it should.
>
> I'm sorry, you often make controversial but somewhat valid arguments about
> inconsistencies in go on this list, but this just isn't one of them. This
> is just an unreasonable complaint.
>
May Go spec is some vague here.
Maybe I should interpret it as following:
when a method is defined for a non-interface type and non-pointer named
type T,
a method with the same name is also defined for type *T, implicitly.
The only difference between the signatures of the two methods is they have
different receiver parameter types,
one receiver type is T, the other is type *T.
The implicit method of *T has only one line of code which is a calling of
the corresponding method of T.
For this example:
type Age int
func (age Age) CanDrink() bool {
age++
return age >= 18
}
// the following method is defined implicitly
/*
func (age *Age) CanDrink() bool {
return (*age).CanDrink()
}
*/
>
>
>
>>
>>
>>>
>>> On Sat, Dec 10, 2016 at 8:17 AM, T L <tapi...@gmail.com> wrote:
>>>
>>>>
>>>> package main
>>>>
>>>> import "fmt"
>>>> import "reflect"
>>>>
>>>> type Age int
>>>> func (age Age) CanDrink() bool {
>>>> age++
>>>> return age >= 18
>>>> }
>>>>
>>>> func main() {
>>>> var age Age = 11
>>>>
>>>> Age.CanDrink(age)
>>>> // (*Age).CanDrink(age) // cannot use age (type Age) as type *Age
>>>> in argument to (*Age).CanDrink
>>>> (*Age).CanDrink(&age)
>>>> fmt.Println(age) // 11
>>>>
>>>> fmt.Println(reflect.TypeOf(Age.CanDrink)) // func(main.Age) bool
>>>> fmt.Println(reflect.TypeOf((*Age).CanDrink)) // func(*main.Age) bool
>>>> }
>>>>
>>>> Why is the parameter of (*Age).CanDrink is a pointer? It is not
>>>> reasonable.
>>>>
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>>>>
>>>
>>> --
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>
>
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