如何为2个（或更多）类型的联合实现接口？

To be more concrete:

I have 2 Readers. One I get from os.Open("someExistingFile") and the other one from strings.NewReader("hello world").

One of them implemets Name(), the other one doesn't. I want to either make the other one also implement Name() (e.g. returning "") or (preferred) only call Name() if the type of the actual parameter supports it.

I hope the code fragment below indicates clearly what I want to solve.

I played around with different receivers, even with reflection but I didn't get to the point ...

package main

import (
    "io"
    "os"
    "strings"
)

func main() {
    stringReader := strings.NewReader("hello world")
    fileReader, _ := os.Open("someExistingFile") // error handling omitted
    fileReader.Name()

    printFilenameIfReaderIsFile(stringReader)
    printFilenameIfReaderIsFile(fileReader)
}

func printFilenameIfReaderIsFile(reader io.Reader) {
    // here I want to ...
    // ... either check if this reader is of type os.File and in this case call its Name() method (preferred)
    // ... or use a custom type instead of io.Reader.
    //     This type's Name() method should return the filename for fileReader and nil for stringReader.
}

You're looking for the type switch control structure.

Your printFilenameIfReaderIsFile function should look like (not actually checked):

func printFilenameIfReaderIsFile(reader io.Reader) {
  switch f := reader.(type) {
    case *os.File:
      // f is now *os.File (not a os.File!)
      fmt.Printf("%s
", f.Name())
  }
}

EDIT: Don't forget, that os.Open returns a *os.File instead of an os.File see docs!