Whats the difference between these two comparison statements?

Question

Whats the difference between these two comparison statments?

var result = EqualityComparer<T>.Default.Equals(@this, null);
var result = @this == null;

Obviously the aim is to test whether the object '@this' isnull.

Answer 1

Well it depends on the type of @this . If it doesn't have an overload of == , the second line will just perform a direct reference comparison, whereas the first line will call an overridden Equals method or an implementation of IEquatable.Equals .

Any sensible implementation will give the same result for both comparisons.

Answer 2

The first statement calls the Equals() method between objects to see if their values are equal, assuming it has been overriden and implemented in the class T . The second statement compares the references instead, unless the == operator has been overridden like in the String class.

Answer 3

operator == calls ReferenceEquals on comparing objects, so compare that objects are pointing to the same memory location.

Equals , instead, is a just virtual method, so can behave differently for different types, as it can be overriden.

For example, for CLR string Equals compares content of a string and not a reference , even if string is a reference type.