映射
Go編程提供的一個重要的數據類型就是映射，唯一映射一個鍵到一個值。一個鍵要使用在以后檢索值的對象。給定的鍵和值，可以在一個Map對象存儲的值。值存儲后，您可以使用它的鍵檢索。
定義映射
必須使用make函數來創建一個映射。
/* 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)
例子
下面的例子說明創建和映射的使用。
package main
import "fmt"
func main {
var coutryCapitalMap map[string]string
/* create a map*/
coutryCapitalMap = 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*/
captial, 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")
}
}
讓我們編譯和運行上面的程序，這將產生以下結果：
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5
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Capital of India is New DelhiCapital of France is ParisCapital of Italy is RomeCapital of Japan is TokyoCapital of United States is not present |
delete() 函數
delete()函數是用于從映射中刪除一個項目。映射和相應的鍵將被刪除。下面是一個例子：
package main
import "fmt"
func main {
/* create a map*/
coutryCapitalMap := 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])
}
}
讓我們編譯和運行上面的程序，這將產生以下結果：
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3
4
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8
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10
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Original MapCapital of France is ParisCapital of Italy is RomeCapital of Japan is TokyoCapital of India is New DelhiEntry for France is deletedUpdated MapCapital of India is New DelhiCapital of Italy is RomeCapital of Japan is Tokyo |
方法
Go編程語言支持特殊類型的函數調用的方法。在方法聲明的語法中，“接收器”的存在是為了表示容器中的函數。該接收器可用于通過調用函數“.”運算符。下面是一個例子：
語法
func (variable_name variable_data_type) function_name() [return_type]{
/* function body*/
}
package main
import (
"fmt"
"math"
)
/* define a circle */
type Circle strut {
x,y,radius float64
}
/* define a method for circle */
func(circle Circle) area() float64 {
return math.Pi * circle.radius * circle.radius
}
func main(){
circle := Circle(x:0, y:0, radius:5)
fmt.Printf("Circle area: %f", circle.area())
}
當上述代碼被編譯和執行時，它產生了以下結果：
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1
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Circle area: 78.539816 |
