On Sat, Feb 5, 2022 at 4:27 PM Kamil Ziemian <kziemian...@gmail.com> wrote:
>
> On the other hand this code compiled
> > package main
> >
> > import "fmt"
> >
> > type Stringer interface {
> > String() string
> > }
> >
> > type StringableVector[T Stringer] []T
> >
> > type someFloat float64
> >
> > func (sF someFloat) String() string {
> > return fmt.Sprintf("someFloat: %v", float64(sF))
> > }
> >
> > func main() {
> > var varStringer Stringer = someFloat(7)
> > sliceSomeFloat := make([]someFloat, 3)
> >
> > var varStringableVector StringableVector[someFloat] = sliceSomeFloat
> >
> > fmt.Printf("varStringer type: %T\n", varStringer)
> > fmt.Printf("sliceSomeFloat type: %T\n", sliceSomeFloat)
> > fmt.Printf("varStringableVector type: %T\n", varStringableVector)
> > }
>
> and produced result
>
> > stringerVar type: main.someFloat
> > sliceScomeFloat type: []main.someFloat
> > stringableVectorVar type: main.StringableVector[main.someFloat]
>
> Variable stringableVectorVar is not of interface type, because in such case
> its type printed by fmt.Printf should be []main.someFloat. So, it looks like
> to me as []main.someFloat is implicitly conversed to
> main.StringableVector[main.someFloat].
>
> Answer to my previous questions was that []stupidFloat/[]someFloat is not of
> type StringableVector[stupidFloat] so it doesn't have method String() string.
> But in my poor understanding of Go, this code shouldn't compile due to
> implicit conversion of two types.
>
> Can anyone explain to me, where am I wrong?
You are not permitted to assign directly from one named type to
another named type. But here you are assigning an unnamed type,
[]someFloat, to a named type, StringableVector[someFloat]. Assigning
an unnamed type to a named type is permitted if the underlying type of
the named is identical to the unnamed type, which in this case it is.
The same is true in non-generic Go. The exact rules are at
https://go.dev/ref/spec#Assignability.
Ian
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