Using type in generic constraint

Question

I'm studying with C# in depth book and it mentions that a form of constraint uses the type parameter in the constraint itself. So what is the difference between these two:

public void Method(AClass<T> myobject) where T : ISomething //Here I say that T has to implement ISomething

public void Method(AClass<T> myobject) where T : ISomething<T> //I don't understand this

Probably what you are asking is duplicate of stackoverflow.com/questions/21186347/…... But the question itself is quite unclear... so not yet closing as duplciate. — Alexei Levenkov
– Alexei Levenkov, Commented Nov 21, 2020 at 1:59

Flydog57 · Accepted Answer · 2020-11-21 06:22:17Z

3

Consider that you have a non-generic interface ISomething defined. The first line constrains T to types that implement that interface.

Now consider that you have a different, generic interface ISomething<T> defined. The second line says that T is constrained to types that implement that interface, but with the further restriction that the generic parameter on the interface must the set to the type that you are specifying.

For example

interface ISomething<T> { /* methods */}

class MyClass: ISomething<MyClass> { /* methods */ }

See the relationship that MyClass has with ISomething<T>. That's what that constraint is demanding.

C++ programmers call this the Curiously Recurring Template Pattern (https://en.m.wikipedia.org/wiki/Curiously_recurring_template_pattern). Don't worry it tends to melt everyone's mind the first time they encounter it. And, if you don't use it for a while, it's not like riding a bike; you need to learn it all over again

answered Nov 21, 2020 at 6:22

Flydog57

7,1712 gold badges22 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Emily Over a year ago

I spent these days reading the few resources I found regarding CRTP with C# and I think the second line means not that T implements the interface, but that the interface can be applied on T, that is, T fulfills the internal restrictions of the interface. What do you think?

Collectives™ on Stack Overflow

Using type in generic constraint

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related