Go語言的struct（結構）為包含多個屬性的資料型態，用來組織多個具有意義的資料。類似物件導向語言(e.g. Java, C++, C$)的類別(class)。
Struct型態使用struct關鍵字來定義，通常搭配type關鍵字使用。
例如下面定義一個Employee struct，裡面有三個欄位(field)分別為ID、Name、Age，然後在main()中以struct literal建立Employee並印出內容。
main.go
package main
import "fmt"
type Employee struct {
ID int64
Name string
Age int
}
func main() {
employee := Employee{1, "John", 33} // create by struct literal
fmt.Println(employee) // {1 John 33}
}
Struct類似Java類別(Class)與實例(instance)的關係。下面是Java程式。
Demo.java
public class Demo {
public static void main(String[] arges) {
Employee employee = new Employee(1, "John", 33); // create instance of class Employee
System.out.println(employee); // Employee{id=1, name='John', age=33}
}
}
class Employee {
private long id;
private String name;
private int age;
public Employee(long id, String name, int age) {
this.id = id;
this.name = name;
this.age = age;
}
@Override
public String toString() {
return "Employee{id=" + id + ", name='" + name + "', age=" + age +"}";
}
}
或是類似JavaScript的Object。下面是JavaScript程式。
demo.js
// define Employee object type by constructor function
function Employee(id, name, age) {
this.id = id;
this.name = name;
this.age = age;
}
let employee = new Employee(1, 'John', 33); // create Employee object
console.log(employee); // Employee {id: 1, name: "John", age: 33}
Struct的屬性使用點號.存取。
main.go
package main
import "fmt"
type Employee struct {
ID int64
Name string
Age int
}
func main() {
employee := Employee{1, "John", 33}
fmt.Println(employee) // {1 John 33}
employee.Age = 26
fmt.Println(employee.Age) // 26
}
也可以先建立一個空的struct然後才設定屬性值。
main.go
package main
import "fmt"
type Employee struct {
ID int64
Name string
Age int
}
func main() {
var employee Employee // create an empty struct Employee
fmt.Println(employee) // {0 0}
employee.Id = 1
employee.Name = "John"
employee.Age = 33
fmt.Println(employee) // {1 John 33}
}
在建立struct時可以指定屬性名稱（不用依照順序）並給於值（稱為struct literals），每個屬性後面要加上逗號,。
main.go
package main
import "fmt"
type Employee struct {
ID int64
Name string
Age int
}
func main() {
employee := Employee{
ID: 1, // don't forget add comma ',' after each value assinment of the field
Name: "John",
Age: 33, // even the last field assinment have to add comma at the end
}
fmt.Println(employee) // {1 John 33}
}
Struct也可以匿名的方式定義及使用，例如下面宣告並建立一個匿名struct。
main.go
package main
import "fmt"
func main() {
employee := struct { // anonymous struct
ID int64
Name string
Age int
} {
ID: 1,
Name: "John",
Age: 33,
}
fmt.Println(employee) // {1 John 33}
}
類似JavaScript以Object literal建立物件。下面是JavaScript程式碼。
demo.js
let employee = {
id: 1,
name: 'John',
age: 33
}
console.log(employee); // {id: 1, name: "John", age: 33}
Struct裡面的屬性也可以是struct。例如下面Employee的屬性的Dept屬性為Department struct型態。
main.go
package main
import "fmt"
type Employee struct {
ID int64
Name string
Age int
Dept Department // nested struct
}
type Department struct {
ID int64
Name string
}
func main() {
employee := Employee{1, "John", 33, Department{2, "HR"}} // create by struct literal
fmt.Println(employee) // {1 John 33 {2 HR}}
}
沒有留言:
張貼留言