Equal sign (==) operator in C#: When does it fail and how to deal with

== operator in C# is very convenient for comparing the equality of two objects. Although the == operator is generally considered to work with all types, it is unusable in some cases.

An example is to compare unconstrained generic types. The code snippet provided in the question bool Compare(T x, T y) { return x == y; } cannot be compiled because it tries to compare two generic parameters of type T. If there are no constraints on T, the type may be a value type, in which case the == operator cannot be applied directly.

For example, the int and float]float operators are not predefined . They use the Equals method for value comparison. On the other hand, reference types such as string have predefined == operators for checking object references.

So, without specifying constraints on T, the compiler cannot determine whether to use the == operator predefined for the reference type, or the Equals method of the value type. To resolve this, T must be constrained to a reference type.

Now, suppose you refer to the type as a type parameter. In this case, the == operator will compare using predefined references, rather than any overloaded version of the operator. This is because predefined citation comparisons are considered more basic and reliable.

If you have insufficient information about type parameters, you can use the IEqualityComparer interface or the EqualityComparer.Default static method. These methods provide a standardized way to compare object equality regardless of their type.