70 lines
1.8 KiB
C
70 lines
1.8 KiB
C
#include <math.h>
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#include <stdio.h>
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// Here's a basic interface for geometric shapes.
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typedef struct {
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double (*area)(void *);
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double (*perim)(void *);
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} geometry;
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// For our example we'll implement this interface on
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// `rect` and `circle` types.
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typedef struct {
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double width, height;
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} rect;
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typedef struct {
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double radius;
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} circle;
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// To implement an interface in C, we need to define functions
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// that match the function pointers in the interface.
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// Here we implement `geometry` on `rect`s.
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double rect_area(void *r) {
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rect *rect_ptr = (rect *)r;
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return rect_ptr->width * rect_ptr->height;
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}
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double rect_perim(void *r) {
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rect *rect_ptr = (rect *)r;
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return 2 * rect_ptr->width + 2 * rect_ptr->height;
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}
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// The implementation for `circle`s.
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double circle_area(void *c) {
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circle *circle_ptr = (circle *)c;
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return M_PI * circle_ptr->radius * circle_ptr->radius;
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}
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double circle_perim(void *c) {
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circle *circle_ptr = (circle *)c;
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return 2 * M_PI * circle_ptr->radius;
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}
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// If a variable has an interface type, then we can call
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// methods that are in the named interface. Here's a
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// generic `measure` function taking advantage of this
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// to work on any `geometry`.
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void measure(void *g, geometry *geom) {
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printf("Area: %f\n", geom->area(g));
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printf("Perimeter: %f\n", geom->perim(g));
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}
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int main() {
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rect r = {.width = 3, .height = 4};
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circle c = {.radius = 5};
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// The `circle` and `rect` struct types both
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// implement the `geometry` interface so we can use
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// instances of these structs as arguments to `measure`.
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geometry rect_geometry = {rect_area, rect_perim};
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geometry circle_geometry = {circle_area, circle_perim};
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printf("Rectangle:\n");
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measure(&r, &rect_geometry);
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printf("\nCircle:\n");
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measure(&c, &circle_geometry);
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return 0;
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}
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