.net - Implementing IEquatable in a base class and use it in all the derived classes -

i have base class implements iequatable interface:

public mustinherit class daobase : implements iequatable(of daobase)          mustoverride function getprimarykey() integer          shadows function equals(other daobase) boolean implements iequatable(of daobase).equals             return getprimarykey() = other.getprimarykey         end function          overrides function gethashcode() integer             return getprimarykey()         end function          ' more things here  end class 

all subclasses must provide getprimarykey method.

public class packaging         inherits daobase      public sub new(id integer)         me.id = id     end sub      overrides function getprimarykey() integer         return id     end function      <daofield> property id integer  end class 

list(of packaging).contains never calls equals method expected.

dim packs new list(of packaging)() dim pack new pack(1) dim pack2 new pack(1) packs.add(pack) 

now, packs.contains(pack) <- true, ok, reference equality

but, packs.contains(pack2) <- false, nok!

i don't want "remember" implement iequatable in derived classes.

is there way force derived implement iequatable, or, better, make contains call base class daobase.equals?

the solution i've found generic-ize base class:

public mustinherit class daobase(of t) : implements iequatable(of t)      mustoverride shadows function equals(other t) boolean implements iequatable(of t).equals     mustoverride overrides function gethashcode() integer  end class  public class packaging     inherits daobase(of packaging)      public sub new(id integer)         me.id = id     end sub      overrides function equals(other packaging) boolean         return gethashcode() = other.gethashcode()     end function      overrides function gethashcode() integer         return id     end function      property id integer end class 

now equals must overridden , specialized on derived type.

    dim p1 new packaging(1)     dim p2 new packaging(1)      dim packs new list(of packaging)     packs.add(c1)      debug.print(packs.contains(c1))         <- true     debug.print(packs.contains(c2))         <- true 

but have write many identical equals methods in derived classes. looking way avoid this.