Map implementation - Code smell in Lookup() & Insert() - go

Question

Below code is Map implementation using array, slice & pointers:
package gomap
import "fmt"
type Entry struct {
stockName string
stockValue float64
}
type bucket []Entry
type Map [4]bucket
type bucketElementPosition [4]int
var emptyPosition = bucketElementPosition{0, 0, 0, 0}
func Newmap() Map {
return Map{} // [(nil,0,0), (nil,0,0), (nil,0,0), (nil,0,0)]
}
func (m *Map) Lookup(key string) float64 {
bucketNumber := (key[0] - 'A') / 7
for _, entry := range m[bucketNumber] { // (*m)[bucketNumber]
if entry.stockName == key {
return entry.stockValue
}
}
return 0
}
func (m *Map) Insert(key string, value float64) {
bucketNumber := (key[0] - 'A') / 7
if cap(m[bucketNumber]) == 0 { // (*m)[bucketNumber]
fmt.Println("bucket number:", bucketNumber)
m[bucketNumber] = make([]Entry, 0, 100)
}
m[bucketNumber] = append(m[bucketNumber], Entry{key, value})
emptyPosition[bucketNumber]++
}
package main
import (
"fmt"
"github.com/myhub/cs61a/gomap"
)
func main() {
var stockData = gomap.Newmap()
(&stockData).Insert("AAPL", 94.56)
(&stockData).Insert("HSCO", 26.72)
(&stockData).Insert("NMZN", 697.45)
(&stockData).Insert("ZSFT", 50.81)
(&stockData).Insert("PMGN", 150.83)
fmt.Println((&stockData).Lookup("AAPL"))
fmt.Println((&stockData).Lookup("HSCO"))
fmt.Println((&stockData).Lookup("NMZN"))
fmt.Println((&stockData).Lookup("ZSFT"))
fmt.Println((&stockData).Lookup("PMGN"))
}
Code smell bucketNumber := (key[0] - 'A') / 7 can be taken care by reading bits and hash.
but for line type bucket []Entry
How to make the concrete type Map, Entry type agnostic? because key is fixed as string and value is fixed as float64

Answer 1

I completed the home assignment like this:
package gomap
import "fmt"
type Entry struct {
key, value interface{}
}
type Map struct {
buckets [4][]Entry
}
func Newmap() *Map {
return &Map{}
}
func (m *Map) bucketNumber(key interface{}) int {
s := fmt.Sprint(key)
return int(s[0]) % len(m.buckets)
}
func (m *Map) Lookup(key interface{}) interface{} {
bucketNumber := m.bucketNumber(key)
for _, entry := range m.buckets[bucketNumber] {
if entry.key == key {
return entry.value
}
}
return nil
}
func (m *Map) Insert(key interface{}, value interface{}) {
bucketNumber := m.bucketNumber(key)
m.buckets[bucketNumber] = append(m.buckets[bucketNumber], Entry{key, value})
}
https://play.golang.org/p/KmVSeDavc3y

Answer 2

There are a few ways you can do that. The most obvious is to use interface{} for key and value. However, there's a type-safe way of doing the keys. You can make Key an interface:
type Key interface {
// Returns the bucket number for the key
BucketNumber() int
// Eq compares the key with the given key
Eq(Key) bool
}
Then you can have an Entry using this key:
type Entry struct {
k Key
v interface{}
}
You can rewrite the map functions to use this key. Value would have to be an interface, and you have to use type assertions to get the underlying value.