Add examples for function dispatch

print_dispatch.c

+/* Compile with:
+CFLAGS="-g -Wall -std=gnu11 -O3" make print_dispatch
+*/
+#define skip_main
+#include "print_methods.c"
+
+textlist_s recipe = {.title="Starfish and Coffee",
+     .len=2, .items=(char*[]){"Starfish", "Coffee"}};
+
+void textlist_print(textlist_s *in){
+    if (in->print){
+        in->print(in);
+        return;
+    }
+
+    printf("Title: %s\n\nItems:\n", in->title);
+    for (int i=0; i< in->len; i++)
+        printf("\t%s\n", in->items[i]);
+}
+
+int main(){
+    textlist_print(&save);
+    printf("\n-----\n\n");
+    textlist_print(&recipe);
+}

print_methods.c

+/* Compile with:
+CFLAGS="-g -Wall -std=gnu11 -O3" make print_methods
+*/
+#include <stdio.h>
+#include "print_typedef.h"
+
+static void print_ad(textlist_s *in){
+    printf("BUY THIS %s!!!! Features:\n", in->title);
+    for (int i=0; i< in->len; i++)
+        printf("∙ %s\n", in->items[i]);
+}
+
+static void print_song(textlist_s *in){
+    printf("♫ %s ♫\nLyrics:\n\n", in->title);
+    for (int i=0; i< in->len; i++)
+        printf("\t%s\n", in->items[i]);
+}
+
+textlist_s save = {.title="God Save the Queen",
+     .len=3, .items=(char*[]){
+    "There's no future", "No future", "No future for me."},
+    .print=print_song};
+
+textlist_s spend = {.title="Never mind the Bollocks LP",
+    .items=(char*[]){"By the Sex Pistols", "Anti-consumption themes"},
+    .len=2, .print=print_ad};
+
+#ifndef skip_main
+int main(){
+    save.print(&save);
+    printf("\n-----\n\n");
+    spend.print(&spend);
+}
+#endif

print_typedef.h

+#ifndef textlist_s_h
+#define textlist_s_h
+
+typedef struct textlist_s {
+    char *title;
+    char **items;
+    int len;
+    void (*print)(struct textlist_s*);
+} textlist_s;
+
+#endif

print_vtable.c

+/* See compilation notes in print_vtable_use.c*/
+#include <stdio.h>
+#include "print_vtable.h"
+
+GHashTable *print_fns;
+
+void check_print_fn(print_fn_type pf) { }
+
+void textlist_print_html(textlist_s *in){
+    if (!print_fns) print_fns = g_hash_table_new(g_direct_hash, g_direct_equal);
+
+    print_fn_type ph = g_hash_table_lookup(print_fns, in->print);
+    if (ph) {
+        ph(in);
+        return;
+    }
+    printf("<title>%s</title>\n<ul>", in->title);
+    for (int i=0; i < in->len; i++)
+        printf("<li>%s</li>\n", in->items[i]);
+    printf("</ul>\n");
+}
+

print_vtable.h

+/* See compilation notes in print_vtable_use.c*/
+#include <glib.h>
+#include "print_typedef.h"
+
+extern GHashTable *print_fns;
+
+typedef void (*print_fn_type)(textlist_s*);
+
+void check_print_fn(print_fn_type pf);
+
+#define print_hash_add(object, print_fn){                         \
+    check_print_fn(print_fn);                                     \
+    g_hash_table_insert(print_fns, (object)->print, print_fn);    \
+}
+
+void textlist_print_html(textlist_s *in);

print_vtable_use.c

+/* Suggested makefile:
+----------
+P=print_vtable_use
+objects=print_vtable.o
+CFLAGS=`pkg-config --cflags glib-2.0` -g -Wall -std=gnu11 -O3
+LDLIBS=`pkg-config --libs   glib-2.0`
+
+$(P): $(objects)
+----------
+*/
+#define skip_main
+#include "print_methods.c"
+#include "print_vtable.h"
+
+static void song_print_html(textlist_s *in){
+    printf("<title>♫ %s ♫</title>\n", in->title);
+    for (int i=0; i < in->len; i++)
+        printf("%s<br>\n", in->items[i]);
+}
+
+int main(){
+    textlist_print_html(&save);
+    printf("\n-----\n\n");
+
+    print_hash_add(&save, song_print_html);
+    textlist_print_html(&save);
+}