Is there a way to New a generic?

Monkey Forums/Monkey Programming/Is there a way to New a generic?

AaronK

(Posted 2011) [#1]

Hi guys, I keep getting an error in a generic class I have when it tries to new an object of it's generic type.



Class Eagle
End

Class Jim<T>

	Method New()
		the = New T()
	End
	Field the:T
End

Function Main()
	Local g:Jim<Eagle> = New Jim<Eagle>
End

Is there a way around this?

muddy_shoes

(Posted 2011) [#2]

Pass the instance in, I suppose:

Class Eagle
End

Class Jim<T>

	Method New( animal:T )
		the = animal
	End
	Field the:T
End

Function Main()
	Local g:Jim<Eagle> = New Jim<Eagle>(New Eagle())
End

AaronK

(Posted 2011) [#3]

Sorry, that example I gave was just an example of the problem. I can't actually pass the instance in in my real program.

Essentially my class holds a collection of T. When I call a particular method with an identifier for T, if an object doesn't exist with that identifier it makes one. Something like

Method Test(objectId:Int)

Local o:T = GetObject(objectId)
if o = Null
o = new T()
InsertIntoCollection(o)
endif

Do something with T.

Of course I can put the test outside in the client code, but I was hoping for my class to handle all that for me.

Cheers

muddy_shoes

(Posted 2011) [#4]

I guess I'd create a TFactory that implements a known interface and pass that in then.

Edit:

Class Eagle
End

Interface AnimalFactory
    Method CreateAnimal:Object()
End

Class EagleFactory Implements AnimalFactory

    Method CreateAnimal:Object()
        Return New Eagle
    End
End

Class Jim<T>
    Method New( af:AnimalFactory )
        factory = af
        the = T(factory.CreateAnimal())
    End
    Field the:T
    Field factory:AnimalFactory
End

Function Main()
    Local g:Jim<Eagle> = New Jim<Eagle>(New EagleFactory())
End

marksibly

(Posted 2011) [#5]

Hi,

No, you can't go 'new T' (or new T[] etc) because as far as the generic code is concerned, 'T' is just 'Object'.