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 ()
{
....
}

"Joe" <jb*******@noemail.noemailwrote in message
news:e0**************@TK2MSFTNGP05.phx.gbl...

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

[puzzlecracker]

On Oct 20, 10:10*am, "Joe" <[e-mail]:

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...

[Peter Duniho]

On Mon, 20 Oct 2008 12:57:26 -0700, puzzlecracker <ir*********@gmail.com>
wrote:

On Oct 20, 10:10Â*am, "Joe" <[e-mail]:

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

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

}

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

Why don't you think that?

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

[puzzlecracker]

On Oct 20, 4:18*pm, "Peter Duniho" <[e-mail]>
wrote:

On Mon, 20 Oct 2008 12:57:26 -0700, puzzlecracker <[e-mail]>*
wrote:

On Oct 20, 10:10*am, "Joe" <[e-mail]:

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...

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]]

puzzlecracker wrote:

On Oct 20, 4:18 pm, "Peter Duniho" <[e-mail]>
wrote:

>On Mon, 20 Oct 2008 12:57:26 -0700, puzzlecracker
<[e-mail]:

>>On Oct 20, 10:10 am, "Joe" <[e-mail]:
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...

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...

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]]

On Oct 20, 10:22*pm, "Ben Voigt [C++ MVP]" <[e-mail]:

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.

For a suggestion of how an alternative might work, see
http://msmvps.com/blogs/jon_skeet/ar...nterfaces.aspx

Jon