C # 8.0 中的空合并赋值运算符
原文:https://www . geesforgeks . org/null-聚结-赋值-运算符-in-c-sharp-8-0/
C# 8.0 引入了一个新的运算符，称为空值合并赋值运算符(？？= )。仅当左侧操作数的值为空时，此运算符用于将其右侧操作数的值赋给左侧操作数。如果左侧操作数的计算结果为非空，则该运算符不计算其右侧操作数。
语法:
p ??= q
这里，p 是左操作数，q 是右操作数？？=运算符。如果 p 的值为空，那么？？=运算符在 p 中指定 q 的值。或者，如果 p 的值非空，则它不计算 q。
要点:
- 的左操作数？？=运算符必须是变量、属性或索引器元素。
- 它是右联想的。
- 你不能称王吗？？=运算符。
-
You are allowed to use ??= operator with reference types and value types.
示例:
```cs // C# program to illustrate how to use // ??= operator with value types and // reference types using System;
namespace example {
class GFG {
static void Main(string[] args) {
// Reference types string item_1 = null; string item_2 = null; string item_4 = "GeeksforGeeks"; string item_5 = "GFG";
// Using ??= operator item_1 = item_1 ??= item_4; string item_6 = item_2 ??= item_5;
Console.WriteLine("Value of item_1 is: {0}\n"+ "Value of item_6 is:{1}", item_1, item_6);
// Value types int ? ele_1 = null;
GFG obj = new GFG();
// Using ??= operator assigns // the value of ele_1 // And also you are allowed to // use method with ??= operator ele_1 = ele_1 ??= obj.Add(10, 30); Console.WriteLine("Value of ele_1 is {0}", ele_1); }
// Method public int Add(int a, int b) { int result = a + b; return result; } } } ```
输出:
```cs Value of item_1 is: GeeksforGeeks Value of item_6 is:GFG Value of ele_1 is 40
```
-
With the help of ??= operator you can remove many redundant “if-else” conditions and make your code more compact and readable. As shown in the below example:
示例:
```cs // C# program to illustrate how to use // ??= operator to remove if statements using System;
namespace example {
class GFG {
// Main Method static void Main(string[] args) { // Nullable variable int ? element = null;
// Checking the element is null or not if (element is null) {
// Assign a new value to the element // Using ??= operator int ? new_element = element ??= 400; Console.WriteLine("Element is null. "+ "So the new element is: {0}", new_element); } } } } ```
输出:
```cs Element is null. So the new element is: 400
```
```cs // C# program to illustrate how to use // ??= operator to remove if statements using System;
namespace example {
class Program { static void Main(string[] args) { // Nullable variable int ? element = null;
// Using ??= operator // Assign values to the null variable element ??= 400; Console.WriteLine("Element is: {0}", element); } } } ```
输出:
cs Element is: 400 -
You can also use ??= operator like a nested chain. It makes your code more readable.
示例:
```cs // C# program to illustrate // how to nest ??= operator using System;
namespace example {
class GFG {
// Main Method static void Main(string[] args) { // Nullable variables int ? ele1 = null; int ? ele2 = null; int ? ele3 = 45;
// Using Nested ??= operator int ? result = ele1 ??= ele2 ??= ele3;
Console.WriteLine("Element is: {0}", result); } } } ```
输出:
cs Element is: 45
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