How to inherit classes that inherits base class more than once

Question

Title is not clear. Here I am explaining

I am having a package say package provide test. It is having classes. I am using Itcl. Package is having following structure

::itcl::class classA {
written something having constructor and methods
}

::itcl::class classB {
inherit ::test::classA
having its own constructor and methods
}

::itcl::class classC {
inherit ::test::classA
having its own constructor and methods
}

::itcl::class classD {
inehrit ::test::classB ::test::classC
having its own constructor and methods
}

When i am requiring package test, I am getting below error

class "::test::classD" inherits base class "::test::classA" more than once:

How can i handle the error

You could try switching to TclOO, which allows this sort of class structure. — Donal Fellows, Apr 16 '14 at 12:18
@DonalFellows: As my framework is using `itcl`. I can't switch to TclOO — Sumit, Apr 17 '14 at 06:00

score 1 · Answer 1 · answered Apr 16 '14 at 10:11

Diamond inheritance is not allowed due to path ambiguity. I.e.

      TopClass
      /       \
LeftClass   RightClass
      \       /
     BottomClass

As workaround you can use composition (has-a) rather than inheritance (is-a).

::itcl::class classA {
}

::itcl::class classB {
    inherit ::test::classA
}

::itcl::class classC {
    inherit ::test::classA
}

::itcl::class classD {
   constructor {} {
     set _b [::test::classB #auto]
     set _c [::test::classC #auto]
   }
   destructor {
     ::itcl::delete $_b
     ::itcl::delete $_c
   }
   private {
      variable _b ""
      variable _c ""
   }
}

Now in classD you must be specific to classB or classC path the code gets to base.

How to inherit classes that inherits base class more than once

1 Answers1