How do I use protocols to implement an OOP type abstract class?

Mrewan79

Apologies if this question has already been asked.

As I understand it, the way to translate a concept similar to use of abstract classes in Elixir is to use Protocols.

For instance if I have an abstract class of “Item” and I want it to be inherited for instance into “Weapon” or “Food” I would like to utilise the methods and values of this class. I do not want the parent methods to be accessed directly, but wish to add additional methods and utilise the child methods in their own way. (i.e. weapons can do damage, food is edible, weapons aren’t).

I can see the documentation here; https://elixir-lang.org/getting-started/protocols.html but am still not totally clear. The examples seem to work like overrides.

4 comments

#protocols #oop #abstractions #how-to-question

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2017-11-02 22:55:10 UTC

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Mrewan79

I used the search tool and nothing came up, but that doesn’t mean the question hasn’t been asked.

Post #1

benwilson512

Author of Craft GraphQL APIs in Elixir with Absinthe

Can you perhaps talk more about the problem you’re trying to solve? The questions you’re asking are sort of the wrong questions in the paradigm that Elixir is. There are no classes, abstract or otherwise, no methods and definitely no parent methods.

If you can talk about about the data you want to represent, and the kinds of functionality you want, we might be able to suggest approaches that better suite a functional paradigm.

Post #2

Mrewan79

#Abstract data examples

#Item - Abstract values
Weight - Int
Size - Int
Name - String
Description - String

#Food
Weight
Size
Name
Description
Edible = true

Post #3

CptnKirk

Protocols aren’t about inheriting data fields, they expose standardized behavior across data types. Think about polymorphic methods in OO languages.

You have a Shape, Circle, Square, Triangle classes. Maybe Shape is an interface or abstract class. It defines certain methods common to the shape family of classes that each subtype must implement. For example, an area() method. Each Shape is able to compute its own area, however, those calculations differ depending on subtype.

With Protocols you can do something similar. You can define a Shape protocol along with protocol implementations for each Square, Circle, Triangle struct you might have. These protocol implementations could be defined within the given modules, or supplied externally in another module. The point is, you can have a function operate on data for which there is a Shape protocol implementation in the same way, regardless of the actual underlying contents of the data.

This is how the Enum module provides standard functionality for processing Enumerable things. Enumerable is a protocol that defines four functions. If you define a protocol implementation that implements those four functions for your data, then you can leverage the Enum module for your data as well.

Post #4

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