src/square.c


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#include <stdlib.h>
#include <stddef.h>
#include "square.h"

struct square
{
    double width;
};

/* Shape interface */

double shape_area_impl(struct shape *shape)
{
    struct square *square = ((void *)shape) + shape_sizeof();
    return square_area(square);
}

void shape_destroy_impl(struct shape *shape)
{
    struct square *square = ((void *)shape) + shape_sizeof();
    square_destroy(square);
}

struct shape *square_as_shape(struct square *square)
{
    return ((void *)square) - shape_sizeof();
}

/* End of shape interface */

struct square *square_create(double width)
{
    struct shape *shape = malloc(shape_sizeof() + sizeof(struct square));
    struct square *square = ((void *)shape) + shape_sizeof();
    square->width = width;

    shape_init(shape, shape_area_impl, shape_destroy_impl);
    return square;
}

double square_area(struct square *square)
{
    return square->width * square->width;
}

void square_destroy(struct square *square)
{
    free(((void *)square) - shape_sizeof());
}