Interface Composition

package main

import (
    "fmt"
)

type RI interface {
    Create(in interface{}) interface{}
    Get(in interface{}) interface{}
    Update(in interface{}) interface{}
    Delete(in interface{}) interface{}
}

type R struct{}

func (r *R) Create(in interface{}) interface{} { return "R Create" }
func (r *R) Get(in interface{}) interface{}    { return "R Get" }
func (r *R) Update(in interface{}) interface{} { return "R Update" }
func (r *R) Delete(in interface{}) interface{} { return "R Delete" }

type RA struct{
    RI
}

func (r *RA) Create(in interface{}) interface{} { return "RA Create" }
func (r *RA) Custom(in interface{}) interface{} { return "RA Custom" }

func newRA() *RA {
    return &RA{RI: &R{}}
}

type SI interface {
    getR() RI
    Create(in interface{}) interface{}
    Get(in interface{}) interface{}
    Update(in interface{}) interface{}
    Delete(in interface{}) interface{}
}

type S struct {
    RI
}

func (s *S) getR() RI { return s.RI }
func (s *S) Create(in interface{}) interface{} { return "S Create " + s.RI.Create(in).(string) }
func (s *S) Get(in interface{}) interface{}    { return "S Get " + s.RI.Get(in).(string) }
func (s *S) Update(in interface{}) interface{} { return "S Update " + s.RI.Update(in).(string) }
func (s *S) Delete(in interface{}) interface{} { return "S Delete " + s.RI.Delete(in).(string) }

func newS(r RI) *S {
        if r == nil {
        r = &R{}
    }
    return &S{RI: r}
}

type SA struct {
    SI
}

func (s *SA) Create(in interface{}) interface{} { return "SA Create " + s.SI.getR().Create(in).(string) }

func newSA() *SA {
    return &SA{SI: newS(newRA())}
}

type SB struct {
    SI
}

func (s *SB) Get(in interface{}) interface{} { return "SB Get " + s.SI.getR().Create(in).(string) }

func newSB() *SB {
    return &SB{SI: newS(nil)}
}

type SC struct {
    SI
}

func (s *SC) Delete(in interface{}) interface{} { return "SC Delete " + s.SI.getR().Create(in).(string) }

func newSC() *SC {
    return &SC{SI: newS(nil)}
}

func process(s SI) {
    fmt.Println(s.Create(123))
    fmt.Println(s.Get(123))
    fmt.Println(s.Update(123))
    fmt.Println(s.Delete(123))
}

func main() {
    process(newSA())
}