Generics, constrains and inheritance

[Joe]

Hi All!

Here's the problem I'm having. I want to create a generic class that
inherits from CollectionBase and implements IBindingList. As part of
IBindingList I have to implement AddNew(). Since this is a generic class the
new throws an error "Cannot create an instance of the variable type 'T'
because it does not have the new constraint".

How do I add a constraint to my class and be able to keep the CollectionBase
and IBindingList?

When I add the where <T>: it means that I want the class T to implement
CollectionBase and IBindingList.

Is it possible to do what I want?

Thanks,
Joe

 

[Joe]

I believe I have my answer. I need to declare my class like this:

class MyClass<T> : CollectionBase, IBindingList where T: new ()
{
....
}

 

[puzzlecracker]

I believe I have my answer. I need to declare my class like this:

class MyClass<T> : CollectionBase, IBindingList where T: new ()
{
    ....

}

I don't think compiler knows what t where T: new () means...

 

[puzzlecracker]

Why don't you think that?

http://msdn.microsoft.com/en-us/library/sd2w2ew5.aspx

I should have rtfm'ed. I didn't know that you can constrain types
based on different constructor types... learn something new every
day...

 

[Ben Voigt [C++ MVP]]

I should have rtfm'ed. I didn't know that you can constrain types
based on different constructor types... learn something new every
day...

You can't. At least not the part about different constructor types. There
is a constraint for "public parameterless constructor" and that's it, sadly.

 

[Jon Skeet [C# MVP]]

You can't.  At least not the part about different constructor types.  There
is a constraint for "public parameterless constructor" and that's it, sadly.

For a suggestion of how an alternative might work, see
http://msmvps.com/blogs/jon_skeet/a...rotocol-buffers-part-4-static-interfaces.aspx

Jon