Null or default comparison of generic argument in C#

Question

I have a generic method defined like this:

public void MyMethod<T>(T myArgument)

The first thing I want to do is check if the value of myArgument is the default value for that type, something like this:

if (myArgument == default(T))

But this doesn't compile because I haven't guaranteed that T will implement the == operator. So I switched the code to this:

if (myArgument.Equals(default(T)))

Now this compiles, but will fail if myArgument is null, which is part of what I'm testing for. I can add an explicit null check like this:

if (myArgument == null || myArgument.Equals(default(T)))

Now this feels redundant to me. ReSharper is even suggesting that I change the myArgument == null part into myArgument == default(T) which is where I started. Is there a better way to solve this problem?

I need to support both references types and value types.

Answer 1

To avoid boxing, the best way to compare generics for equality is with EqualityComparer<T>.Default. This respects IEquatable<T> (without boxing) as well as object.Equals, and handles all the Nullable<T> "lifted" nuances. Hence:

if(EqualityComparer<T>.Default.Equals(obj, default(T))) {
    return obj;
}

This will match:

• null for classes
• null (empty) for Nullable<T>
• zero/false/etc for other structs