Test for equality to the default value

c# generics equality
Greg picture Greg · Dec 13, 2009 · Viewed 22k times · Source

The following doesn't compile:

public void MyMethod<T>(T value)
{
    if (value == default(T))
    {
        // do stuff
    }
}

Error: Operator '==' cannot be applied to operands of type 'T' and 'T'

I can't use value == null because T may be a struct.
I can't use value.Equals(default(T)) because value may be null.
What is the proper way to test for equality to the default value?

Answer

Marc Gravell picture Marc Gravell · Dec 13, 2009

To avoid boxing for struct / Nullable<T>, I would use:

if (EqualityComparer<T>.Default.Equals(value,default(T)))
{
    // do stuff
}

This supports any T that implement IEquatable<T>, using object.Equals as a backup, and handles null etc (and lifted operators for Nullable<T>) automatically.

There is also Comparer<T>.Default which handles comparison tests. This handles T that implement IComparable<T>, falling back to IComparable - again handling null and lifted operators.

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