Go: How to embed same interface twice? - go

Question

Suppose we have something like this:
type ReadHandler interface {
Reader
Reader
}
Obviously, it will cause ambiguity when we call members of Reader interface on instances of ReadHandeler. So how can we achieve this in Golang?

Answer 1

1- Use io.MultiReader, see func MultiReader(readers ...Reader) Reader Docs:
MultiReader returns a Reader that's the logical concatenation of the
provided input readers. They're read sequentially. Once all inputs
have returned EOF, Read will return EOF. If any of the readers
return a non-nil, non-EOF error, Read will return that error.
2- or name it:
type ReadHandler interface {
Read(p []byte) (n int, err error)
Read2(p []byte) (n int, err error)
}
or:
type ReadHandler interface {
io.Reader
Read2(p []byte) (n int, err error)
}
Demonstration working sample code:
package main
import (
"errors"
"fmt"
"io"
)
func main() {
s := my{[]byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, []byte{10, 20, 30, 40, 50}}
buf := make([]byte, 5)
n, e := s.Read(buf)
fmt.Println(n, e, buf)
n, e = s.Read2(buf)
fmt.Println(n, e, buf)
}
type ReadHandler interface {
io.Reader
Read2(p []byte) (n int, err error)
}
type my struct {
buf []byte
buf2 []byte
}
func (t *my) Read(p []byte) (n int, err error) {
if len(p) > len(t.buf) {
return 0, errors.New("len(p)>len(buf)")
}
m := copy(p, t.buf)
return m, nil
}
func (t *my) Read2(p []byte) (n int, err error) {
if len(p) > len(t.buf2) {
return 0, errors.New("len(p)>len(buf2)")
}
m := copy(p, t.buf2)
return m, nil
}
Output:
5 <nil> [1 2 3 4 5]
5 <nil> [10 20 30 40 50]
3- name it:
Looking for a general solution to embed an interface (with any number
of methods), twice in a struct.
type my struct {
io.Reader
Rdr2 io.Reader
}
or
type my struct {
Rdrs []io.Reader
}