ad1.go

package main

import (
    "fmt"
    "sync"
)

type LegacyService struct {
}

func (l *LegacyService) ExpensiveOperation(arg string) string {
    // some expensive operation
    return "result"
}

type Service interface {
    Do(arg string) string
}

type ServiceAdapter struct {
    LegacyService
    cache map[string]string
    mutex sync.RWMutex
}

func NewServiceAdapter() *ServiceAdapter {
    return &ServiceAdapter{
        cache: make(map[string]string),
    }
}

func (s *ServiceAdapter) Do(arg string) string {
    s.mutex.RLock()
    res, ok := s.cache[arg]
    s.mutex.RUnlock()
    if ok {
        return res
    }

    res = s.ExpensiveOperation(arg)

    s.mutex.Lock()
    s.cache[arg] = res
    s.mutex.Unlock()
    return res
}

func main() {
    adapter := NewServiceAdapter()
    fmt.Println(adapter.Do("arg"))
    fmt.Println(adapter.Do("arg"))
}