对？的行为感到困惑。算子 [英] Confused about behavior of ?. operator

问题描述

这是我的代码

class Address
{
    public bool IsAppartment { get; set; }
}

class Employee
{
    public string Name { get; set; }
    public Address Address { get; set; }
}    
class Program
{
    static void Main(string[] args)
    {
        Employee employee = new Employee()
        {
            Name = "Charlie"
        };
        if (employee.Address?.IsAppartment ?? true)
        {
            Console.WriteLine("Its an apartment");
        }
        else
        {
            Console.WriteLine("No employee address or not an apartment");
        }
    }
}

该程序的输出

它的公寓

Its an apartment

？。 运算符

如果条件成员或元素链中的一个操作访问
操作返回null，则链的其余部分不执行。

if one operation in a chain of conditional member or element access operations returns null, the rest of the chain doesn't execute.

在这种情况下，Address对象为null，我不明白为什么它不在代码的else分支中？

In this case, Address object is null, I don't understand why it's not going in the else branch of the code here?

更新

下面的等效代码是什么

UPDATE
What will be equivalent code for following using short cut operators?

if (employee.Address != null && employee.Address.IsAppartment == true)
{
    Console.WriteLine("Its an apartment");
}
else
{
    Console.WriteLine("No employee address or not an apartment");
}

推荐答案

这是正确的，其余的链中的不执行，空伙伴运算符 ?? 返回 true 。根据 MSDN

This is correct, the rest of the chain doesn't execute, null-coalescing operator ?? returns true. According to MSDN

null-coalescing运算符??如果不为null，则返回其左侧
操作数的值；否则，它将评估右侧的
操作数并返回其结果。

The null-coalescing operator ?? returns the value of its left-hand operand if it isn't null; otherwise, it evaluates the right-hand operand and returns its result.

如果要将结果与任何一个进行比较 true 或 false （根据您的更新），您可以使用

If you want to compare the result with either true or false (per your update) you can use

if (employee?.Address?.IsAppartment == true)
{
}

左侧操作数返回 Nullable< bool> ，您也可以在 MSDN

The left-hand operand returns Nullable<bool>, you can also read about it in MSDN

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