Add barebones-combined

Author: TotallyNotChase

barebones-combined.c

@@ -0,0 +1,88 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* The `Show` typeclass allows types to be turned into their string representation */
+typedef struct
+{
+    char* (*const show)(void* self);
+} ShowTC;
+
+typedef struct
+{
+    void* self;
+    ShowTC const* tc;
+} Show;
+
+
+/* The `Enum` typeclass allows types to be enumerable */
+typedef struct
+{
+    int (*const from_enum)(void* self);
+} EnumTC;
+
+typedef struct
+{
+    void* self;
+    EnumTC const* tc;
+} Enum;
+
+
+/* Typeclass that asks for both `Show` and `Enum` implementation */
+typedef struct
+{
+    void* self;
+    ShowTC const* showtc;
+    EnumTC const* enumtc;
+} ShowEnum;
+
+void print_shen(ShowEnum shen)
+{
+    char* const s = shen.showtc->show(shen.self);
+    int enm = shen.enumtc->from_enum(shen.self);
+    printf("%s : %d\n", s, enm);
+    free(s);
+}
+
+/* The `show` function implementation for `int` */
+static char* int_show(int* x)
+{
+    /*
+    Note: The `show` function of a `Show` typeclass is expected to return a malloc'ed value
+    The users of a generic `Show` are expected to `free` the returned pointer from the function `show`.
+    */
+    size_t len = snprintf(NULL, 0, "%d", *x);
+    char* const res = malloc((len + 1) * sizeof(*res));
+    snprintf(res, len + 1, "%d", *x);
+    return res;
+}
+
+/* Make function to build a generic `Show` out of a concrete type- `int` */
+Show int_to_show(int* x)
+{
+    /* Build the vtable once and attach a pointer to it every time */
+    static ShowTC const tc = {.show = (char* (*const)(void*))(int_show) };
+    return (Show){.tc = &tc, .self = x};
+}
+
+/* The `from_enum` function implementation for `int` */
+static int int_from_enum(int* x)
+{
+    return *x;
+}
+
+/* Make function to build a generic `Show` out of a concrete type- `int` */
+Enum int_to_enum(int* x)
+{
+    /* Build the vtable once and attach a pointer to it every time */
+    static EnumTC const tc = {.from_enum = (int (*const)(void*))(int_from_enum) };
+    return (Enum){.tc = &tc, .self = x};
+}
+
+int main(void)
+{
+    int x = 42;
+    ShowEnum shen = { .self = &x, .showtc = int_to_show(&x).tc, .enumtc = int_to_enum(&x).tc };
+    print_shen(shen);
+    return 0;
+}