src/cx/iterator.h

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2021 Mike Becker, Olaf Wintermann All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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 */
/**
 * @file iterator.h
 * @brief Interface for iterator implementations.
 * @author Mike Becker
 * @author Olaf Wintermann
 * @copyright 2-Clause BSD License
 */

#ifndef UCX_ITERATOR_H
#define UCX_ITERATOR_H

#include "common.h"

#ifdef __cplusplus
extern "C" {
#endif

/**
 * Common data for all iterators.
 */
struct cx_iterator_base_s {
    /**
     * True iff the iterator points to valid data.
     */
    bool (*valid)(const void *);

    /**
     * Returns a pointer to the current element.
     *
     * When valid returns false, the behavior of this function is undefined.
     */
    void *(*current)(const void *);

    /**
     * Original implementation in case the function needs to be wrapped.
     */
    void *(*current_impl)(const void *);

    /**
     * Advances the iterator.
     *
     * When valid returns false, the behavior of this function is undefined.
     */
    void (*next)(void *);
    /**
     * Indicates whether this iterator may remove elements.
     */
    bool mutating;
    /**
     * Internal flag for removing the current element when advancing.
     */
    bool remove;
};

/**
 * Declares base attributes for an iterator.
 * Must be the first member of an iterator structure.
 */
#define CX_ITERATOR_BASE struct cx_iterator_base_s base

/**
 * Internal iterator struct - use CxIterator.
 */
struct cx_iterator_s {
    /**
     * Inherited common data for all iterators.
     */
    CX_ITERATOR_BASE;

    /**
     * Handle for the current element.
     */
    void *elem_handle;

    /**
     * Handle for the source collection, if any.
     */
    union {
        /**
         * Access for mutating iterators.
         */
        void *m;
        /**
         * Access for normal iterators.
         */
        const void *c;
    } src_handle;

    /**
     * If the iterator is position-aware, contains the index of the element in the underlying collection.
     * Otherwise, this field is usually uninitialized.
     */
    size_t index;

    /**
     * The size of an individual element.
     */
    size_t elem_size;

    /**
     * May contain the total number of elements, if known.
     * Shall be set to @c SIZE_MAX when the total number is unknown during iteration.
     */
    size_t elem_count;
};

/**
 * Iterator type.
 *
 * An iterator points to a certain element in a (possibly unbounded) chain of elements.
 * Iterators that are based on collections (which have a defined "first" element), are supposed
 * to be "position-aware", which means that they keep track of the current index within the collection.
 *
 * @note Objects that are pointed to by an iterator are always mutable through that iterator. However,
 * any concurrent mutation of the collection other than by this iterator makes this iterator invalid,
 * and it must not be used anymore.
 */
typedef struct cx_iterator_s CxIterator;

/**
 * Checks if the iterator points to valid data.
 *
 * This is especially false for past-the-end iterators.
 *
 * @param iter the iterator
 * @retval true if the iterator points to valid data
 * @retval false if the iterator already moved past the end
 */
#define cxIteratorValid(iter) (iter).base.valid(&(iter))

/**
 * Returns a pointer to the current element.
 *
 * The behavior is undefined if this iterator is invalid.
 *
 * @param iter the iterator
 * @return a pointer to the current element
 * @see cxIteratorValid()
 */
#define cxIteratorCurrent(iter) (iter).base.current(&iter)

/**
 * Advances the iterator to the next element.
 *
 * @param iter the iterator
 */
#define cxIteratorNext(iter) (iter).base.next(&iter)

/**
 * Flags the current element for removal, if this iterator is mutating.
 *
 * Does nothing for non-mutating iterators.
 *
 * @param iter the iterator
 */
#define cxIteratorFlagRemoval(iter) (iter).base.remove |= (iter).base.mutating

/**
 * Obtains a reference to an arbitrary iterator.
 *
 * This is useful for APIs that expect some iterator as an argument.
 *
 * @param iter the iterator
 * @return (@c CxIterator*) a pointer to the iterator
 */
#define cxIteratorRef(iter) &((iter).base)

/**
 * Loops over an iterator.
 *
 * @param type the type of the elements
 * @param elem the name of the iteration variable
 * @param iter the iterator
 */
#define cx_foreach(type, elem, iter) \
for (type elem; cxIteratorValid(iter) && (elem = (type)cxIteratorCurrent(iter)) != NULL ; cxIteratorNext(iter))


/**
 * Creates an iterator for the specified plain array.
 *
 * The @p array can be @c NULL in which case the iterator will be immediately
 * initialized such that #cxIteratorValid() returns @c false.
 *
 * This iterator yields the addresses of the array elements.
 * If you want to iterator over an array of pointers, you can
 * use cxIteratorPtr() to create an iterator which directly
 * yields the stored pointers.
 *
 * @param array a pointer to the array (can be @c NULL)
 * @param elem_size the size of one array element
 * @param elem_count the number of elements in the array
 * @return an iterator for the specified array
 * @see cxIteratorPtr()
 */
cx_attr_nodiscard
cx_attr_export
CxIterator cxIterator(
        const void *array,
        size_t elem_size,
        size_t elem_count
);

/**
 * Creates a mutating iterator for the specified plain array.
 *
 * While the iterator is in use, the array may only be altered by removing
 * elements through #cxIteratorFlagRemoval(). Every other change to the array
 * will bring this iterator to an undefined state.
 *
 * When @p remove_keeps_order is set to @c false, removing an element will only
 * move the last element to the position of the removed element, instead of
 * moving all subsequent elements by one. Usually, when the order of elements is
 * not important, this parameter should be set to @c false.
 *
 * The @p array can be @c NULL in which case the iterator will be immediately
 * initialized such that #cxIteratorValid() returns @c false.
 *
 *
 * @param array a pointer to the array (can be @c NULL)
 * @param elem_size the size of one array element
 * @param elem_count the number of elements in the array
 * @param remove_keeps_order @c true if the order of elements must be preserved
 * when removing an element
 * @return an iterator for the specified array
 */
cx_attr_nodiscard
cx_attr_export
CxIterator cxMutIterator(
        void *array,
        size_t elem_size,
        size_t elem_count,
        bool remove_keeps_order
);

/**
 * Creates an iterator for the specified plain pointer array.
 *
 * This iterator assumes that every element in the array is a pointer
 * and yields exactly those pointers during iteration (while in contrast
 * an iterator created with cxIterator() would return the addresses
 * of those pointers within the array).
 *
 * @param array a pointer to the array (can be @c NULL)
 * @param elem_count the number of elements in the array
 * @return an iterator for the specified array
 * @see cxIterator()
 */
cx_attr_nodiscard
cx_attr_export
CxIterator cxIteratorPtr(
        const void *array,
        size_t elem_count
);

/**
 * Creates a mutating iterator for the specified plain pointer array.
 *
 * This is the mutating variant of cxIteratorPtr(). See also
 * cxMutIterator().
 *
 * @param array a pointer to the array (can be @c NULL)
 * @param elem_count the number of elements in the array
 * @param remove_keeps_order @c true if the order of elements must be preserved
 * when removing an element
 * @return an iterator for the specified array
 * @see cxMutIterator()
 * @see cxIteratorPtr()
 */
cx_attr_nodiscard
cx_attr_export
CxIterator cxMutIteratorPtr(
        void *array,
        size_t elem_count,
        bool remove_keeps_order
);

#ifdef __cplusplus
} // extern "C"
#endif

#endif // UCX_ITERATOR_H