C＃泛型约束

Question

I am having trouble with a generic type constraint. I have the below method, and im struggling to pass anything into the childSegments parameter, the first parameter i can get round.

private void FillSegment<T, TT>(BaseSegment<T> segment, IEnumerable<BaseSegment<TT>> childSegments)
        where T : class
        where TT : class
    {}

TT is of type class, but the list im trying to pass in, should be a combination of different classes not just a single class type, that's the wall i am hitting. I could just pass in this list:

List<BaseSegment<Lead>> l = new List<BaseSegment<Lead>>();

but like i said, i need to pass in multiple classes, i have a LeadSegment, AccountSegment, ContactSegment etc (which implement BaseSegment<T> ).

The ideal scenario would be something like this:

List<BaseSegment<T>> lst = new List<BaseSegment<T>>();
lst.Add(LeadSegment);
lst.Add(AccountSegment);
lst.Add(ContactSegment);

..and pass that, but you cannot create a list with a <T> type within a method or outside i believe

Any Ideas?

Thanks

Answer 1

Make BaseSegment a non-generic abstract class (you don't ever instantiate BaseSegment directly do you?). Your signature for FillSegment could then look like this:

private void FillSegment<TParent>(TParent parent, IEnumerable<BaseSegment> children)
    where TParent : BaseSegment

This enables you to consume the method like this:

var parent = new SomeParentSegment(); // SomeParentSegment derives from BaseSegment
var children = new List<BaseSegment>();
children.Add(new LeadSegment()); // LeadSegment derives from BaseSegment
children.Add(new AccountSegment()); // AccountSegment derives from BaseSegment
children.Add(new ContactSegment()); // ContactSegment derives from BaseSegment

FillSegment(parent, children);

Note that this allows children to be of the same type as parent , given that both instances derive from BaseSegment .

Answer 2

I'm having a little trouble following what you are wanting to do, but I think you want to make your constraints

where TT : T

or...

where TT : BaseSegment<T>

Both of these scenarios enable your "Ideal scenario" above; but without a further understanding...