mapの操作

sample.go

package main

import "fmt"

func main() {
  fmt.Println( "withNilMap" )
  withNilMap()
  fmt.Println( "withMakeMap" )
  withMakeMap()
  fmt.Println( "withEmptyInitMap" )
  withEmptyInitMap()
  fmt.Println( "withInitMap" )
  withInitMap()
}

func withNilMap() {
  var m map[string]int
  fmt.Println( m )
  fmt.Println( m[ "hoge" ] )
  // m[ "hoge" ] = 1
  fmt.Println( m == nil )
}

func withMakeMap() {
  m := make( map[string]int )
  fmt.Println( m )
  fmt.Println( m[ "hoge" ] )
}

func withEmptyInitMap() {
  m := map[string]int{}
  fmt.Println( m )
  fmt.Println( m[ "hoge" ] )
}

func withInitMap() {
  m := map[string]int{
    "hoge": 1,
    "fuga": 2,
  }
  fmt.Println( m )
  fmt.Println( m[ "hoge" ] )

  v1, b1 := m[ "hoge" ]
  fmt.Println( v1, b1 )
  v2, b2 := m[ "abc" ]
  fmt.Println( v2, b2 )
}