Messing with interfaces in VimL

interface.vim

" Messing with interfaces
" Barry Arthur, Oct 2015

function! Foo()
  let obj = {}
  func obj.register(a, b)
    echo string(a:a) . ' and ' . string(a:b)
  endfunc
  return obj
endfunction

let x = Foo()

function! Bar(x)
  let obj = {}
  let obj.z = a:x
  func obj.doit(a, b)
    call call(self.z.register, [a:a, a:b], self)
  endfunc
  return obj
endfunction

let y = Bar(x)

call y.doit({'i' : 1}, {'j' : 2})