c# - Is there a difference between x is null and ReferenceEquals(x, null)?

Question

When I write this:

ReferenceEquals(x, null)

Visual studio suggests that the

null check can be simplified.

and simplifies it to

x is null

Are those really the same?

Answer 1

I noticed a lot of answers specifying that x == null, x is null, and ReferenceEquals(x, null) are all equivalent - and for most cases this is true. However, there is a case where you CANNOT use x == null as I have documented below:

Note that the code below assumes you have implemented the Equals method for your class:

Do NOT do this - the operator == method will be called recursively until a stack overflow occurs:

public static bool operator ==(MyClass x1, MyClass x2)
{
   if (x1 == null)
      return x2 == null;

   return x1.Equals(x2)
}

Do this instead:

public static bool operator ==(MyClass x1, MyClass x2)
{
   if (x1 is null)
      return x2 is null;

   return x1.Equals(x2)
}

Or

public static bool operator ==(MyClass x1, MyClass x2)
{
   if (ReferenceEquals(x1, null))
      return ReferenceEquals(x2, null);

   return x1.Equals(x2)
}