C# public class where T : class, Class, new() 混淆

Question

I am new to C# and I am faced with a class with this structure:

public class SimpleGetter<TSubs> : GetterBase<TSubs>, ISubscriptionsSingleGetter<TSubs>
    where TSubs : class, ISimpleSubscription, new()
{
    UserSubscriptionsResponse<TSubs> ISubscriptionsSingleGetter<TSubs>.Get()
    {
        return ((ISubscriptionsSingleGetter<TSubs>)this).Get(null);
    }

    UserSubscriptionsResponse<TSubs> ISubscriptionsSingleGetter<TSubs>.Get(string userId)
    {
        return GetSubsResponse(userId);
    }
}

I need to pass userID to the get() function (if possible), but I am confused on how to do that. I have tried to do some research on this but I do not even know what this way of defining a class is called. I come from objective c where things seem more straight forward.

Answer 1

I do not even know what this way of defining a class is called

This is a generic class.

  public class SimpleGetter<TSubs> : GetterBase<TSubs>, ISubscriptionsSingleGetter<TSubs>
    where TSubs : class, ISimpleSubscription, new()

which has one generic type parameter TSubs . This class inherits the GetterBase<TSubs> and implements the interface ISubscriptionsSingleGetter<TSubs> . Furthermore, the TSubs must be a reference type and must have a parameterless constructor, which implements the ISimpleSubscription interface.

public class FakeSubs : ISimpleSubscription
{
    public FakeSubs()
    {

    }

    // Here you have to implement ISimpleSubscription. 
    // You could also define any properties, methods etc.
}

// Now you could use your generic class as below:

var simpleGetter = new SimpleGetter<FakeSubs>();

Having created the above instance, you can call the Get method as Tewr , pointed out in his comment:

var response = ((ISubscriptionsSingleGetter<FakeSubs>)simpleGetter).Get(42);

Answer 2

Just to complement Christos' answer and help you understand the syntax a bit better, let's break the class definition term by term.

public - visible to all callers.

class - a reference type (ie not a struct ).

SimpleGetter<TSubs> - the class name is SimpleGetter, and it is generic with respect to the parameter TSubs.

: GetterBase<TSubs> - it inherits from a base class which is itself generic with respect to the parameter TSubs.

, ISubscriptionsSingleGetter<TSubs> - and it also implements the generic interface ISubscriptionSingleGetter.

where TSubs: - there are some constraints on the type which the generic parameter TSubs must be of.

class - it must itself also be a reference type.

ISimpleSubscription - it must implement this (non-generic) interface.

new() - it must have a public parameterless constructor.