On 2/11/22 9:54 am, Julieta Shem wrote:
But we've left behind a more basic requirement --- the Stack
class wishes for all the methods already written in some class called
Pair,
Is that *really* what you want, though?
To my way of thinking, a Stack and a Pair are quite different
data structures, each having their own characteristic operations.
Things I want to be able to do with a Stack:
- Create an empty stack
- Push an item onto the top of the stack
- Pop an item off the top of the stack
Things I want to be able to do with a Pair:
- Create a pair containing two given objects
- Get the first item
- Get the second item
I don't see any overlap between these at the conceptual level.
Possibly I might want to use Pairs as part of the *implementation*
of a stack, but that doesn't mean that any Pair methods should
appear as Stack methods.
Here's how I might do this in a functional style using Python:
class Pair:
def __init__(self, first, second):
self._first = first
self._second = second
def first(self):
return self._first
def second(self):
return self._second
class Stack:
def __init__(self):
self._data = None
def push(self, item):
result = Stack()
result._data = Pair(item, self._data)
return result
def pop(self):
rest = Stack()
rest._data = self._data.second()
return self._data.first(), rest
Note that neither Stack nor Pair inherits from the other.
--
Greg
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