How to make LINQ's Max-function return the default value if the sequence is empty?

Try this:

var myList = new List<int>();
var max = myList.DefaultIfEmpty().Max();
Console.Write(max);

LINQ's DefaultIfEmpty-method checks if the sequence is empty. If that is the case, it will return a singleton sequence: A sequence containing exactly one element. This one element has the default value of the sequence's type. If the sequence does contain elements, the DefaultIfEmpty-method will simply return the sequence itself.

See the MSDN for further information

• on the Enumerable.DefaultIfEmpty<TSource> method and
• the default keyword in generic code.

What about an extension?

public static int MaxOrDefault<T>(this IEnumerable<T> enumeration, Func<T, int> selector)
{
    return enumeration.Any() ? enumeration.Max(selector) : default(int);
}

Slightly at a tangent but perhaps still useful..another solution is to cast the value to nullable type;

var myInt = new Int[0].Max(i=>(int?)i);//myInt == null