Go提供了另一個重要的數(shù)據(jù)類型：映射(Map)，它將唯一鍵映射到值。 鍵是用于在檢索值的對象。 給定一個鍵和一個值就可以在Map對象中設(shè)置值。設(shè)置存儲值后，就可以使用其鍵檢索它對應(yīng)的值了。

定義映射

必須要使用make函數(shù)來創(chuàng)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(chuàng)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(zhí)行時，它產(chǎn)生以下結(jié)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(shù)

delete()函數(shù)用于從映射中刪除項目。它需要映射以及指定要刪除的相應(yīng)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(zhí)行時，它產(chǎn)生以下結(jié)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