#544 – Specifying a Constraint for a Type Parameter

When you provide a type parameter to a generic class, you can only invoke methods in System.Object for objects of that type.

    public class Dog<TFavThing>
    {
        public void BuryThing(TFavThing thing)
        {
            // Err: TFavThing does not contain a definition for Bury
            thing.Bury();
        }

You can allow calling methods in a specific type by adding a constraint to the type parameter, indicating what type the parameter must conform to.  Adding a constraint lets you do two things:

  • Ensure that a type parameter belongs to a specific type
  • Allow you to call methods in a specific type, for objects whose type matches the type parameter

A constraint consists of a type parameter name following by an indication of the type that it must be.  (Generally a base class or an interface).

    // TFavThing type parameter must be a type that implements IBuryable
    public class Dog<TFavThing> where TFavThing: IBuryable
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About Sean
Software developer in the Twin Cities area, passionate about software development and sailing.

3 Responses to #544 – Specifying a Constraint for a Type Parameter

  1. Pingback: #546 – Specifying More than One Constraint for the Same Type Parameter « 2,000 Things You Should Know About C#

  2. Pingback: #547 – Things That Can Serve as Type Parameter Constraints « 2,000 Things You Should Know About C#

  3. Pingback: #1,070 – A Generic Type Can Be Compiled | 2,000 Things You Should Know About C#

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