在Go中，如何将某个接口的切片传递给期望有其他兼容接口的切片？ [重复]

Question

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• Type converting slices of interfaces 5 answers

I have two interfaces, A and B. It happens that A includes B. Finally, I have a concrete implementation of A (call it Impl), which, by definition, also implements B.

For example:

type A interface {
    Close() error
    Read(b []byte) (int, error)
}

type Impl struct {}
func (I Impl) Read(b []byte) (int, error) {
    fmt.Println("In read!")
    return 10, nil
}
func (I Impl) Close() error {
    fmt.Println("I am here!")
    return nil
}

Since A requires Read(), and Impl implements A, it also satisfies io.Reader.

If I try to pass individual items across functions, it works fine. But if I try slices of A to functions expecting io.Reader, it fails.

Example:

func single(r io.Reader) {
    fmt.Println("in single")
}
func slice(r []io.Reader) {
    fmt.Println("in slice")
}
im := &Impl{}

// works
single(im)

// FAILS!
list := []A{t}
slice(list)

If I can pass an A to single(r io.Reader), why can I not pass []A to slice(r []io.Reader), and how would I correct it?

Actual implementation at https://play.golang.org/p/QOREQJTQhD just uncomment the last two lines in main() and the error shows:

main.go:38: cannot use list (type []A) as type []io.Reader in argument to slice

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Answer 1

I kind of asked something similar here In Go, how can I make a generic function with slices?

Sadly, this is definitely a weakness in Go. The only way for you to go around this is to make a new slice of type []io.Reader with elements from []A