Initial commit.

example/cat.h

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+/*
+ * This file is part of libooc.
+ * https://xw3.org/hanez/libooc
+ *
+ * Copyright 2026 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2.0
+ */
+
+#ifndef CAT_H
+#define CAT_H
+
+#include "animal.h"
+
+typedef struct Cat Cat;
+
+/*
+ * Derived class.
+ *
+ * The embedded Animal comes first, so a Cat pointer can be handed to any
+ * function expecting an Animal, and Cat adds a colour and a private `_lives` of
+ * its own.
+ *
+ * Two things follow from that ordering. The ooc_object header inside Animal
+ * stays at offset zero, where the library looks for it, and the upcast is a
+ * no-op cast because both addresses are the same -- which is what lets speak()
+ * in cat.c cast its Animal * back to a Cat * without arithmetic. The cost is
+ * that a Cat may not add a member of its own before the base.
+ *
+ * The struct holds no destructor of its own; the one Cat registers lives in
+ * Cat_class and releases both the colour and Animal's name.
+ */
+struct Cat {
+    Animal animal;
+    char  *colour;
+
+    /*
+     * Private to Cat, and readable by name: one leading underscore stops
+     * ooc_set() from writing it but leaves ooc_get() alone. Animal's `_id` works
+     * the same way, so the rule is the one in the library rather than something
+     * the subclass has to repeat.
+     */
+    int    _lives;
+};
+
+/*
+ * Cat's runtime type record, the value ooc_new() takes.
+ *
+ * Its `super` is Animal_class, so a Cat inherits Animal's fields, and its
+ * `size` is sizeof(Cat), so the allocation has room for the colour and the
+ * lives count.
+ */
+extern const ooc_class Cat_class;
+
+/*
+ * Create a Cat named `name` of the given `colour` and return it, or NULL.
+ *
+ * The result has a reference count of one, so ownership is the caller's and it
+ * must reach ooc_release() eventually. Returns NULL if any step of the
+ * construction fails, leaving nothing to release.
+ *
+ * The object is a Cat and answers to Cat's `speak`, whether it is later reached
+ * through a Cat * or an Animal *.
+ */
+Cat *cat_new(const char *name, int age, const char *colour);
+
+#endif /* CAT_H */