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This chapter will handle topics about LINQ.

Using is and as instead of OfType

Using is and as cast should not be used in LINQ as it degrades readability and to some extend also performance (neglactable small under normal circumstances).

Bad Less readable and unnecessary casts.

persons.Where(p => p is FullTimeEmployee).Select(p => p as FullTimeEmployee);
persons.Where(p => p is FullTimeEmployee).Select(p => (FullTimeEmployee)p);
persons.Select(p => p as FullTimeEmployee).Where(p => p != null);

Good Using OfType is cleaner and more readable.


Using Count() instead of All or Any

The problem with Count() is that LINQ has to enumerate every single entry in the enumeration to get the full count, where as Any/All would return immediately as soon as the condition is not satisfied anymore. In general conditions (excluding LINQ to SQL) Any/All in the worst case have the same runtime as Count but in best and average cases they are faster and more readable.

Bad Less readable and unnecessary enumerations

persons.Count() > 0
persons.Count(MyPredicate) > 0
persons.Count(MyPredicate) == 0
persons.Count(MyPredicate) == persons.Count()

Good More readable and avoids unnecessary enumerations