polymorphism simulation in c

polymorph.c

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>


typedef struct __attribute__((__packed__)) greetable {
    void (*greet)(struct greetable* this);
} Greetable; // interface

typedef struct __attribute__((__packed__)) person {
    void (*greet)(struct person* this);
    char* name;
} Person; // class

typedef struct __attribute__((__packed__)) worker {
    void (*greet)(struct worker* this);
    char* name;
    int workedHours;
} Worker; // class extends Person

typedef struct __attribute__((__packed__)) teacher {
    void (*greet)(struct teacher* this);
    char* name;
    int teachedHours;
    int students; 
} Teacher; // class extends Person

// methods.
void person_greet(Person* this) { printf("Hello im - %s\n", this->name); }
void worker_greet(Worker* this) {
    printf("Hello im a worker %s and i worked %d hours\n", this->name, this->workedHours);
}
void teacher_greet(Teacher* this) {
    printf("Hello im teacher %s with %d students, teached for %d hours.\n", this->name, this->students, this->teachedHours);
}

// constructors
Person* person_new(char* name) {
    Person* p = calloc(1, sizeof(Person));
    p->name = malloc(strlen(name)+1);
    strcpy(p->name, name);
    p->greet = person_greet;
    return p;
}

Teacher* teacher_new(char* name, int teachedHours, int students) {
    Teacher* t = calloc(1, sizeof(Teacher));
    Person* super = person_new(name); // super(name)
    memcpy(t, super, sizeof(Person)); free(super);
    t->teachedHours = teachedHours;
    t->students = students;
    t->greet = teacher_greet;
    return t;
}

Worker* worker_new(char* name, int workedHours) {
    Worker* t = calloc(1, sizeof(Worker));
    Person* super = person_new(name); // super(name)
    memcpy(t, super, sizeof(Person)); free(super);
    t->workedHours = workedHours;
    t->greet = worker_greet;
    return t;
}

int main()
{
    
    printf("Through person polymorphism:\n");
    Person* people[] = {
        (Person*) person_new("Jozo"),
        (Person*) teacher_new("Jurgen", 69, 16),
        (Person*) worker_new("Vaclav", 420)
    };
    
    for (int i = 0; i < 3; i++) {
        people[i]->greet(people[i]);
    }
    
    
    printf("\nGreetable polymorphism cast:\n");
    Greetable* greeters[3]; // cast array
    for (int i = 0; i < 3; i++) greeters[i] = (Greetable*) people[i];
    
    for (int i = 0; i < 3; i++) {
        greeters[i]->greet(greeters[i]);
    }

    return 0;
}