How to Prevent Infinite Recursion When Overloading the == Operator with Null Values?

Handling null values ​​when overloading the == operator

In some cases, trying to overload the == operator with the following code may result in infinite recursion:

<code class="language-c#">Foo foo1 = null;
Foo foo2 = new Foo();
Assert.IsFalse(foo1 == foo2);

public static bool operator ==(Foo foo1, Foo foo2) {
    return foo1 == null ? foo2 == null : foo1.Equals(foo2);
}</code>

The problem is that without specific null checking, the == comparison recursively calls the == operator overloaded method to compare foo1 and foo2. Since foo1 is empty, a recursive loop is triggered.

To solve this problem, you can use ReferenceEquals to add a null value check:

<code class="language-c#">Foo foo1 = null;
Foo foo2 = new Foo();
Assert.IsFalse(foo1 == foo2);

public static bool operator ==(Foo foo1, Foo foo2) {
    if (object.ReferenceEquals(null, foo1))
        return object.ReferenceEquals(null, foo2);
    return foo1.Equals(foo2);
}</code>

By using ReferenceEquals to check for null values, you ensure that the == operator overloaded method does not recur infinitely, allowing null comparisons to be handled gracefully.

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