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