What is "Checkpoint: The Code So Far (After LSP)" about?

A running snapshot of the bird hierarchy after the Liskov Substitution Principle: Flyable and Eater interfaces replace the broken FlyingBird/NotFlyingBird split, shown file by file.

What topics does "Checkpoint: The Code So Far (After LSP)" cover?

This article covers: liskov substitution principle, lsp checkpoint, solid principles, flyable interface, polymorphism example, oop design patterns.

LSP Checkpoint: Flyable and Eater Interfaces in Code

This is a running snapshot, not a new lesson. It's everything the bird hierarchy looks like after the previous posts: a penguin that can't fly, and a sparrow that can't eat, both handled correctly.

Interfaces mark behavior. Classes mark identity. That split is what makes this work.

main.cpp

#include <vector>
#include "bird/classes/Bird.h"
#include "bird/interfaces/Flyable.h"
#include "bird/classes/Crow.h"
#include "bird/classes/Sparrow.h"
#include "bird/classes/Owl.h"
#include "bird/classes/Pigeon.h"
#include "bird/classes/Penguin.h"

int main() {
    Crow crow("Crow", "black", 2);
    Sparrow sparrow("Sparrow", "brown", 1);
    Owl owl("Owl", "brown", 3);
    Pigeon pigeon("Pigeon", "grey", 2);
    Penguin penguin("Penguin", "black-and-white", 4);

    std::vector<Bird*> allBirds = { &crow, &sparrow, &owl, &pigeon, &penguin };
    for (Bird* bird : allBirds) {
        bird->walk();
    }

    std::vector<Flyable*> fliers = { &crow, &sparrow, &owl, &pigeon };
    for (Flyable* bird : fliers) {
        bird->fly();
    }

    crow.eat();
    pigeon.eat();

    return 0;
}