How can I make sure that FirstOrDefault has returned a value

Question

Here\'s a simplified version of what I\'m trying to do:

var days = new Dictionary();
days.Add(1, \"Monday\");
days.Add(2, \"Tuesday\");
..         


        

Answer 1

FirstOrDefault doesn't return null, it returns default(T).
You should check for:

var defaultDay = default(KeyValuePair);
bool b = day.Equals(defaultDay);

From MSDN - Enumerable.FirstOrDefault:

default(TSource) if source is empty; otherwise, the first element in source.

Notes:

• If your code is generic it is better to use EqualityComparer.Default.Equals(day, defaultDay), becuase .Equals may be overridden or day could be a null.
• In C# 7.1 you will be able to use KeyValuePair defaultDay = default;, see Target-typed "default" literal.
• See also: Reference Source - FirstOrDefault