src/include/nodes/pg_list.h

/*-------------------------------------------------------------------------
 *
 * pg_list.h
 *	  interface for PostgreSQL generic linked list package
 *
 * This package implements singly-linked homogeneous lists.
 *
 * It is important to have constant-time length, append, and prepend
 * operations. To achieve this, we deal with two distinct data
 * structures:
 *
 *		1. A set of "list cells": each cell contains a data field and
 *		   a link to the next cell in the list or NULL.
 *		2. A single structure containing metadata about the list: the
 *		   type of the list, pointers to the head and tail cells, and
 *		   the length of the list.
 *
 * We support three types of lists:
 *
 *	T_List: lists of pointers
 *		(in practice usually pointers to Nodes, but not always;
 *		declared as "void *" to minimize casting annoyances)
 *	T_IntList: lists of integers
 *	T_OidList: lists of Oids
 *
 * (At the moment, ints and Oids are the same size, but they may not
 * always be so; try to be careful to maintain the distinction.)
 *
 * There is also limited support for lists of TransactionIds; since these
 * are used in only one or two places, we don't provide a full implementation,
 * but map them onto Oid lists.  This effectively assumes that TransactionId
 * is no wider than Oid and both are unsigned types.
 *
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/include/nodes/pg_list.h,v 1.55 2006/08/27 19:11:46 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef PG_LIST_H
#define PG_LIST_H

#include "nodes/nodes.h"


typedef struct ListCell ListCell;

typedef struct List
{
	NodeTag		type;			/* T_List, T_IntList, or T_OidList */
	int			length;
	ListCell   *head;
	ListCell   *tail;
} List;

struct ListCell
{
	union
	{
		void	   *ptr_value;
		int			int_value;
		Oid			oid_value;
	}			data;
	ListCell   *next;
};

/*
 * The *only* valid representation of an empty list is NIL; in other
 * words, a non-NIL list is guaranteed to have length >= 1 and
 * head/tail != NULL
 */
#define NIL						((List *) NULL)

/*
 * These routines are used frequently. However, we can't implement
 * them as macros, since we want to avoid double-evaluation of macro
 * arguments. Therefore, we implement them using GCC inline functions,
 * and as regular functions with non-GCC compilers.
 */
#ifdef __GNUC__

static __inline__ ListCell *
list_head(List *l)
{
	return l ? l->head : NULL;
}

static __inline__ ListCell *
list_tail(List *l)
{
	return l ? l->tail : NULL;
}

static __inline__ int
list_length(List *l)
{
	return l ? l->length : 0;
}
#else

extern ListCell *list_head(List *l);
extern ListCell *list_tail(List *l);
extern int	list_length(List *l);
#endif   /* __GNUC__ */

/*
 * NB: There is an unfortunate legacy from a previous incarnation of
 * the List API: the macro lfirst() was used to mean "the data in this
 * cons cell". To avoid changing every usage of lfirst(), that meaning
 * has been kept. As a result, lfirst() takes a ListCell and returns
 * the data it contains; to get the data in the first cell of a
 * List, use linitial(). Worse, lsecond() is more closely related to
 * linitial() than lfirst(): given a List, lsecond() returns the data
 * in the second cons cell.
 */

#define lnext(lc)				((lc)->next)
#define lfirst(lc)				((lc)->data.ptr_value)
#define lfirst_int(lc)			((lc)->data.int_value)
#define lfirst_oid(lc)			((lc)->data.oid_value)

#define linitial(l)				lfirst(list_head(l))
#define linitial_int(l)			lfirst_int(list_head(l))
#define linitial_oid(l)			lfirst_oid(list_head(l))

#define lsecond(l)				lfirst(lnext(list_head(l)))
#define lsecond_int(l)			lfirst_int(lnext(list_head(l)))
#define lsecond_oid(l)			lfirst_oid(lnext(list_head(l)))

#define lthird(l)				lfirst(lnext(lnext(list_head(l))))
#define lthird_int(l)			lfirst_int(lnext(lnext(list_head(l))))
#define lthird_oid(l)			lfirst_oid(lnext(lnext(list_head(l))))

#define lfourth(l)				lfirst(lnext(lnext(lnext(list_head(l)))))
#define lfourth_int(l)			lfirst_int(lnext(lnext(lnext(list_head(l)))))
#define lfourth_oid(l)			lfirst_oid(lnext(lnext(lnext(list_head(l)))))

#define lfifth(l)				lfirst(lnext(lnext(lnext(lnext(list_head(l))))))
#define lfifth_int(l)			lfirst_int(lnext(lnext(lnext(lnext(list_head(l))))))
#define lfifth_oid(l)			lfirst_oid(lnext(lnext(lnext(lnext(list_head(l))))))
#define lcfifth(l)				lnext(lnext(lnext(lnext(list_head(l)))))

#define llast(l)				lfirst(list_tail(l))
#define llast_int(l)			lfirst_int(list_tail(l))
#define llast_oid(l)			lfirst_oid(list_tail(l))

/*
 * Convenience macros for building fixed-length lists
 */
#define list_make1(x1)				lcons(x1, NIL)
#define list_make2(x1,x2)			lcons(x1, list_make1(x2))
#define list_make3(x1,x2,x3)		lcons(x1, list_make2(x2, x3))
#define list_make4(x1,x2,x3,x4)		lcons(x1, list_make3(x2, x3, x4))

#define list_make1_int(x1)			lcons_int(x1, NIL)
#define list_make2_int(x1,x2)		lcons_int(x1, list_make1_int(x2))
#define list_make3_int(x1,x2,x3)	lcons_int(x1, list_make2_int(x2, x3))
#define list_make4_int(x1,x2,x3,x4) lcons_int(x1, list_make3_int(x2, x3, x4))

#define list_make1_oid(x1)			lcons_oid(x1, NIL)
#define list_make2_oid(x1,x2)		lcons_oid(x1, list_make1_oid(x2))
#define list_make3_oid(x1,x2,x3)	lcons_oid(x1, list_make2_oid(x2, x3))
#define list_make4_oid(x1,x2,x3,x4) lcons_oid(x1, list_make3_oid(x2, x3, x4))

/*
 * Limited support for lists of TransactionIds, mapped onto lists of Oids
 */
#define lfirst_xid(lc)				((TransactionId) lfirst_oid(lc))
#define lappend_xid(list, datum)	lappend_oid(list, (Oid) (datum))

/*
 * foreach -
 *	  a convenience macro which loops through the list
 */
#define foreach(cell, l)	\
	for ((cell) = list_head(l); (cell) != NULL; (cell) = lnext(cell))

/*
 * for_each_cell -
 *	  a convenience macro which loops through a list starting from a
 *	  specified cell
 */
#define for_each_cell(cell, initcell)	\
	for ((cell) = (initcell); (cell) != NULL; (cell) = lnext(cell))

#define foreach_with_count(cell, list, counter) \
	for ((cell) = list_head(list), (counter)=0; \
	     (cell) != NULL; \
	     (cell) = lnext(cell), ++(counter))


/*
 * forboth -
 *	  a convenience macro for advancing through two linked lists
 *	  simultaneously. This macro loops through both lists at the same
 *	  time, stopping when either list runs out of elements. Depending
 *	  on the requirements of the call site, it may also be wise to
 *	  assert that the lengths of the two lists are equal.
 */
#define forboth(cell1, list1, cell2, list2)							\
	for ((cell1) = list_head(list1), (cell2) = list_head(list2);	\
		 (cell1) != NULL && (cell2) != NULL;						\
		 (cell1) = lnext(cell1), (cell2) = lnext(cell2))

extern List *lappend(List *list, void *datum);
extern List *lappend_int(List *list, int datum);
extern List *lappend_oid(List *list, Oid datum);

extern ListCell *lappend_cell(List *list, ListCell *prev, void *datum);
extern ListCell *lappend_cell_int(List *list, ListCell *prev, int datum);
extern ListCell *lappend_cell_oid(List *list, ListCell *prev, Oid datum);

extern List *lcons(void *datum, List *list);
extern List *lcons_int(int datum, List *list);
extern List *lcons_oid(Oid datum, List *list);

extern List *list_concat(List *list1, List *list2);
extern List *list_truncate(List *list, int new_size);

extern ListCell *list_nth_cell(List *list, int n);
extern void *list_nth(List *list, int n);
extern int	list_nth_int(List *list, int n);
extern Oid	list_nth_oid(List *list, int n);

extern int list_find(List *list, void *datum);
extern int list_find_ptr(List *list, void *datum);
extern int list_find_int(List *list, int datum);
extern int list_find_oid(List *list, Oid datum);

extern bool list_member(List *list, void *datum);
extern bool list_member_ptr(List *list, void *datum);
extern bool list_member_int(List *list, int datum);
extern bool list_member_oid(List *list, Oid datum);

extern List *list_delete(List *list, void *datum);
extern List *list_delete_ptr(List *list, void *datum);
extern List *list_delete_int(List *list, int datum);
extern List *list_delete_oid(List *list, Oid datum);
extern List *list_delete_first(List *list);
extern List *list_delete_cell(List *list, ListCell *cell, ListCell *prev);

extern List *list_union(List *list1, List *list2);
extern List *list_union_ptr(List *list1, List *list2);
extern List *list_union_int(List *list1, List *list2);
extern List *list_union_oid(List *list1, List *list2);

extern List *list_intersection(List *list1, List *list2);

/* currently, there's no need for list_intersection_int etc */

extern List *list_difference(List *list1, List *list2);
extern List *list_difference_ptr(List *list1, List *list2);
extern List *list_difference_int(List *list1, List *list2);
extern List *list_difference_oid(List *list1, List *list2);

extern List *list_append_unique(List *list, void *datum);
extern List *list_append_unique_ptr(List *list, void *datum);
extern List *list_append_unique_int(List *list, int datum);
extern List *list_append_unique_oid(List *list, Oid datum);

extern List *list_concat_unique(List *list1, List *list2);
extern List *list_concat_unique_ptr(List *list1, List *list2);
extern List *list_concat_unique_int(List *list1, List *list2);
extern List *list_concat_unique_oid(List *list1, List *list2);

extern List *list_reverse_ints(List *list);

extern void list_free(List *list);
extern void list_free_deep(List *list);

extern List *list_copy(List *list);
extern List *list_copy_tail(List *list, int nskip);

extern void *list_nth_replace(List *list, int n, void *new_data);

/*
 * To ease migration to the new list API, a set of compatibility
 * macros are provided that reduce the impact of the list API changes
 * as far as possible. Until client code has been rewritten to use the
 * new list API, the ENABLE_LIST_COMPAT symbol can be defined before
 * including pg_list.h
 */
#ifdef ENABLE_LIST_COMPAT

#define lfirsti(lc)					lfirst_int(lc)
#define lfirsto(lc)					lfirst_oid(lc)

#define makeList1(x1)				list_make1(x1)
#define makeList2(x1, x2)			list_make2(x1, x2)
#define makeList3(x1, x2, x3)		list_make3(x1, x2, x3)
#define makeList4(x1, x2, x3, x4)	list_make4(x1, x2, x3, x4)

#define makeListi1(x1)				list_make1_int(x1)
#define makeListi2(x1, x2)			list_make2_int(x1, x2)

#define makeListo1(x1)				list_make1_oid(x1)
#define makeListo2(x1, x2)			list_make2_oid(x1, x2)

#define lconsi(datum, list)			lcons_int(datum, list)
#define lconso(datum, list)			lcons_oid(datum, list)

#define lappendi(list, datum)		lappend_int(list, datum)
#define lappendo(list, datum)		lappend_oid(list, datum)

#define nconc(l1, l2)				list_concat(l1, l2)

#define nth(n, list)				list_nth(list, n)

#define member(datum, list)			list_member(list, datum)
#define ptrMember(datum, list)		list_member_ptr(list, datum)
#define intMember(datum, list)		list_member_int(list, datum)
#define oidMember(datum, list)		list_member_oid(list, datum)

/*
 * Note that the old lremove() determined equality via pointer
 * comparison, whereas the new list_delete() uses equal(); in order to
 * keep the same behavior, we therefore need to map lremove() calls to
 * list_delete_ptr() rather than list_delete()
 */
#define lremove(elem, list)			list_delete_ptr(list, elem)
#define LispRemove(elem, list)		list_delete(list, elem)
#define lremovei(elem, list)		list_delete_int(list, elem)
#define lremoveo(elem, list)		list_delete_oid(list, elem)

#define ltruncate(n, list)			list_truncate(list, n)

#define set_union(l1, l2)			list_union(l1, l2)
#define set_uniono(l1, l2)			list_union_oid(l1, l2)
#define set_ptrUnion(l1, l2)		list_union_ptr(l1, l2)

#define set_difference(l1, l2)		list_difference(l1, l2)
#define set_differenceo(l1, l2)		list_difference_oid(l1, l2)
#define set_ptrDifference(l1, l2)	list_difference_ptr(l1, l2)

#define equali(l1, l2)				equal(l1, l2)
#define equalo(l1, l2)				equal(l1, l2)

#define freeList(list)				list_free(list)

#define listCopy(list)				list_copy(list)

extern int	length(List *list);
#endif   /* ENABLE_LIST_COMPAT */

/**
 * If listPtrPtr is non-NULL, and *listPtrPtr is non-NULL then free the list and set *listPtrPtr to NULL
 *
 * @param listPtr a ptr to a list object.  May be NULL, and may also point to NULL
 */
static inline
void freeListAndNull(List **listPtrPtr)
{
	if ( listPtrPtr && *listPtrPtr)
	{
		list_free(*listPtrPtr);
		*listPtrPtr = NULL;
	}
}

#endif   /* PG_LIST_H */