Parametric Polymorphism in C#

Question 1

What are the upsides of C# generics?

Answer 1

no type erasure in binaries, which enables:

1. Better optimization (for example, no need for boxing and unboxing)
2. Better reflection support

Question 2

What are the downsides of C# generics? and what are the solutions?

Answer 2

It might have caused code segment to dramatically increase in size
Solution #1 – Types are instantiated on demand (at run-time – CLR feature)
Solution #2 – All reference types share the same IL code

Question 3

What is the default C# generics variance?

Answer 3

no-variance.

Question 4

What is a delegate in C#?

Answer 4

delegate is pretty much a function pointer type.
hence the syntax is easy to remember:
public delegate object ConversionDelegate(string d);
(same as a function just add delegate at the begining).

Question 5

Does C# support co-variance and contra-variance for generics?

Answer 5

yes. only for interfaces and delegates not classes.

applies only for reference types.

Question 6

What is the out generic modifier in C#?

Answer 6

Specifies that the type parameter is only used to return values from methods, hence covariance is safe!

Question 7

What is the in generic modifier in C#?

Answer 7

Specifies that the type parameter is only used to pass arguments into the methods, hence contra-variant is safe!