Question

So I was looking at the MSDN example here: Constraints on Type Parameters (C# Programming Guide) and the 1st example shows the following generic class defining a where constraint with a single concrete type: Employee

public class GenericList<T> where T : Employee

Now when using a where constraint I totally understand the use when defining > 1 type, or most certainly when using an Interface. However (and I know it was only an example), why would I ever want to just use a where constraint to restrict to a single concrete type? Couldn’t I just replace the code below:

public T FindFirstOccurrence(string s)

with the following since there is only a single constraint anyway?

public Employee FindFirstOccurrence(string s)

The only reason I could see deploying code with a single where constriant is for flexibility in the future to add additional constraints for if Employee became IEmployee and I was set up a bit easier for the changes.

Can someone explain what purpose using a where constraint for a single type provides?

Thanks!

Answer 1

why would I ever want to just use a where constraint to restrict to a single concrete type?

Not quite right there – the constraint is on the Employee type and any type that inherits from it, so it can apply to Manager and CEO classes as well.

Defining the constraint means you can use any accessible methods on the Employee type inside your code, whether the passes in type is an Employee or an inheriting type.