Sealed classes and methods: Difference between revisions

← Older edit Newer edit →

Content deleted Content added

Inline

@@ Line 27: / Line 27: @@
 It has structs rather than classes which are just a collection of fields. Methods on a struct can be simulated by functions whose first argument is a pointer to the struct.
-However, there is no way to simulate inheritance of one struct by another. A struct can contain a field of another struct type but this is not the same as 'struct embedding' in the Go language.
+To simulate inheritance, one can embed a 'parent' field ''first'' in the 'child' struct and then pass the address of that field to 'parent' methods.
+However, there is no way that the method can tell whether it's receiving a pointer to a 'parent' instance or a pointer to a 'child' field. To use the Wren technique for simulating sealed methods, we therefore need to pass a further parameter, namely a type identifier, as the following code illustrates.
-So, for the purposes of this task, we can say that structs and simulated methods in C are by their nature always sealed.
+<syntaxhighlight lang="c">#include <stdio.h>
+typedef enum {
+    PARENT,
+    CHILD
+} typeid;
+typedef struct {
+    const char* name;
+    int age;
+} parent;
+typedef struct {
+    parent p;
+} child;
+void watchMovie(parent *p, typeid id) {
+    if (id == PARENT) {
+        printf("%s is watching the movie...\n", p->name);
+    } else if (id == CHILD) {
+        if (p->age < 15) {
+            printf("Sorry, %s, you are too young to watch the movie.\n", p->name);
+        } else {
+            printf("%s is watching the movie...\n", p->name);
+        }
+    }
+}
+int main() {
+    parent p = { "Donald", 42 };
+    child c1 = { "Lisa", 18 };
+    child c2 = { "Fred", 10 };
+    watchMovie(&p, PARENT);
+    watchMovie(&c1.p, CHILD);
+    watchMovie(&c2.p, CHILD);
+}</syntaxhighlight>
+{{out}}
+<pre>
+Donald is watching the movie...
+Lisa is watching the movie...
+Sorry, Fred, you are too young to watch the movie.
+</pre>
 =={{header|FreeBASIC}}==