Go語言映射

Go提供了另一個重要的數據類型：映射(Map)，它將唯一鍵映射到值。 鍵是用於在檢索值的對象。 給定一個鍵和一個值就可以在Map對象中設置值。設置存儲值後，就可以使用其鍵檢索它對應的值了。

定義映射

必須要使用make函數來創建映射。

/* declare a variable, by default map will be nil*/
var map_variable map[key_data_type]value_data_type

/* define the map as nil map can not be assigned any value*/
map_variable = make(map[key_data_type]value_data_type)

示例

以下示例說明了映射的創建和使用。

package main

import "fmt"

func main() {
   var countryCapitalMap map[string]string
   /* create a map*/
   countryCapitalMap = make(map[string]string)

   /* insert key-value pairs in the map*/
   countryCapitalMap["France"] = "Paris"
   countryCapitalMap["Italy"] = "Rome"
   countryCapitalMap["Japan"] = "Tokyo"
   countryCapitalMap["India"] = "New Delhi"

   /* print map using keys*/
   for country := range countryCapitalMap {
      fmt.Println("Capital of",country,"is",countryCapitalMap[country])
   }

   /* test if entry is present in the map or not*/
   capital, ok := countryCapitalMap["United States"]
   /* if ok is true, entry is present otherwise entry is absent*/
   if(ok){
      fmt.Println("Capital of United States is", capital)  
   }else {
      fmt.Println("Capital of United States is not present") 
   }
}

當上述代碼編譯和執行時，它產生以下結果：

Capital of India is New Delhi
Capital of France is Paris
Capital of Italy is Rome
Capital of Japan is Tokyo
Capital of United States is not present

delete()函數

delete()函數用於從映射中刪除項目。它需要映射以及指定要刪除的相應鍵。 以下是示例：

package main

import "fmt"

func main() {   
   /* create a map*/
   countryCapitalMap := map[string] string {"France":"Paris","Italy":"Rome","Japan":"Tokyo","India":"New Delhi"}

   fmt.Println("Original map")   

   /* print map */
   for country := range countryCapitalMap {
      fmt.Println("Capital of",country,"is",countryCapitalMap[country])
   }

   /* delete an entry */
   delete(countryCapitalMap,"France");
   fmt.Println("Entry for France is deleted")  

   fmt.Println("Updated map")   

   /* print map */
   for country := range countryCapitalMap {
      fmt.Println("Capital of",country,"is",countryCapitalMap[country])
   }
}

當上述代碼編譯和執行時，它產生以下結果：

Original Map
Capital of France is Paris
Capital of Italy is Rome
Capital of Japan is Tokyo
Capital of India is New Delhi
Entry for France is deleted
Updated Map
Capital of India is New Delhi
Capital of Italy is Rome
Capital of Japan is Tokyo