pg_list.h

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/*-------------------------------------------------------------------------
 *
 * pg_list.h
 *    interface for PostgreSQL generic list package
 *
 * Once upon a time, parts of Postgres were written in Lisp and used real
 * cons-cell lists for major data structures.  When that code was rewritten
 * in C, we initially had a faithful emulation of cons-cell lists, which
 * unsurprisingly was a performance bottleneck.  A couple of major rewrites
 * later, these data structures are actually simple expansible arrays;
 * but the "List" name and a lot of the notation survives.
 *
 * One important concession to the original implementation is that an empty
 * list is always represented by a null pointer (preferentially written NIL).
 * Non-empty lists have a header, which will not be relocated as long as the
 * list remains non-empty, and an expansible data array.
 *
 * We support four 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
 *  T_XidList: lists of TransactionIds
 *      (the XidList infrastructure is less complete than the other cases)
 *
 * (At the moment, ints, Oids, and XIDs are the same size, but they may not
 * always be so; be careful to use the appropriate list type for your data.)
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/nodes/pg_list.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef PG_LIST_H
#define PG_LIST_H
 
#include "nodes/nodes.h"
 
 
typedef union ListCell
{
    void       *ptr_value;
    int         int_value;
    Oid         oid_value;
    TransactionId xid_value;
} ListCell;
 
typedef struct List
{
    NodeTag     type;           /* T_List, T_IntList, T_OidList, or T_XidList */
    int         length;         /* number of elements currently present */
    int         max_length;     /* allocated length of elements[] */
    ListCell   *elements;       /* re-allocatable array of cells */
    /* We may allocate some cells along with the List header: */
    ListCell    initial_elements[FLEXIBLE_ARRAY_MEMBER];
    /* If elements == initial_elements, it's not a separate allocation */
} List;
 
/*
 * The *only* valid representation of an empty list is NIL; in other
 * words, a non-NIL list is guaranteed to have length >= 1.
 */
#define NIL                     ((List *) NULL)
 
/*
 * State structs for various looping macros below.
 */
typedef struct ForEachState
{
    const List *l;              /* list we're looping through */
    int         i;              /* current element index */
} ForEachState;
 
typedef struct ForBothState
{
    const List *l1;             /* lists we're looping through */
    const List *l2;
    int         i;              /* common element index */
} ForBothState;
 
typedef struct ForBothCellState
{
    const List *l1;             /* lists we're looping through */
    const List *l2;
    int         i1;             /* current element indexes */
    int         i2;
} ForBothCellState;
 
typedef struct ForThreeState
{
    const List *l1;             /* lists we're looping through */
    const List *l2;
    const List *l3;
    int         i;              /* common element index */
} ForThreeState;
 
typedef struct ForFourState
{
    const List *l1;             /* lists we're looping through */
    const List *l2;
    const List *l3;
    const List *l4;
    int         i;              /* common element index */
} ForFourState;
 
typedef struct ForFiveState
{
    const List *l1;             /* lists we're looping through */
    const List *l2;
    const List *l3;
    const List *l4;
    const List *l5;
    int         i;              /* common element index */
} ForFiveState;
 
/*
 * These routines are small enough, and used often enough, to justify being
 * inline.
 */
 
/* Fetch address of list's first cell; NULL if empty list */
static inline ListCell *
list_head(const List *l)
{
    return l ? &l->elements[0] : NULL;
}
 
/* Fetch address of list's last cell; NULL if empty list */
static inline ListCell *
list_tail(const List *l)
{
    return l ? &l->elements[l->length - 1] : NULL;
}
 
/* Fetch address of list's second cell, if it has one, else NULL */
static inline ListCell *
list_second_cell(const List *l)
{
    if (l && l->length >= 2)
        return &l->elements[1];
    else
        return NULL;
}
 
/* Fetch list's length */
static inline int
list_length(const List *l)
{
    return l ? l->length : 0;
}
 
/*
 * Macros to access the data values within List cells.
 *
 * Note that with the exception of the "xxx_node" macros, these are
 * lvalues and can be assigned to.
 *
 * 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 list cell.
 */
#define lfirst(lc)              ((lc)->ptr_value)
#define lfirst_int(lc)          ((lc)->int_value)
#define lfirst_oid(lc)          ((lc)->oid_value)
#define lfirst_xid(lc)          ((lc)->xid_value)
#define lfirst_node(type,lc)    castNode(type, lfirst(lc))
 
#define linitial(l)             lfirst(list_nth_cell(l, 0))
#define linitial_int(l)         lfirst_int(list_nth_cell(l, 0))
#define linitial_oid(l)         lfirst_oid(list_nth_cell(l, 0))
#define linitial_node(type,l)   castNode(type, linitial(l))
 
#define lsecond(l)              lfirst(list_nth_cell(l, 1))
#define lsecond_int(l)          lfirst_int(list_nth_cell(l, 1))
#define lsecond_oid(l)          lfirst_oid(list_nth_cell(l, 1))
#define lsecond_node(type,l)    castNode(type, lsecond(l))
 
#define lthird(l)               lfirst(list_nth_cell(l, 2))
#define lthird_int(l)           lfirst_int(list_nth_cell(l, 2))
#define lthird_oid(l)           lfirst_oid(list_nth_cell(l, 2))
#define lthird_node(type,l)     castNode(type, lthird(l))
 
#define lfourth(l)              lfirst(list_nth_cell(l, 3))
#define lfourth_int(l)          lfirst_int(list_nth_cell(l, 3))
#define lfourth_oid(l)          lfirst_oid(list_nth_cell(l, 3))
#define lfourth_node(type,l)    castNode(type, lfourth(l))
 
#define llast(l)                lfirst(list_last_cell(l))
#define llast_int(l)            lfirst_int(list_last_cell(l))
#define llast_oid(l)            lfirst_oid(list_last_cell(l))
#define llast_xid(l)            lfirst_xid(list_last_cell(l))
#define llast_node(type,l)      castNode(type, llast(l))
 
/*
 * Convenience macros for building fixed-length lists
 */
#define list_make_ptr_cell(v)   ((ListCell) {.ptr_value = (v)})
#define list_make_int_cell(v)   ((ListCell) {.int_value = (v)})
#define list_make_oid_cell(v)   ((ListCell) {.oid_value = (v)})
#define list_make_xid_cell(v)   ((ListCell) {.xid_value = (v)})
 
#define list_make1(x1) \
    list_make1_impl(T_List, list_make_ptr_cell(x1))
#define list_make2(x1,x2) \
    list_make2_impl(T_List, list_make_ptr_cell(x1), list_make_ptr_cell(x2))
#define list_make3(x1,x2,x3) \
    list_make3_impl(T_List, list_make_ptr_cell(x1), list_make_ptr_cell(x2), \
                    list_make_ptr_cell(x3))
#define list_make4(x1,x2,x3,x4) \
    list_make4_impl(T_List, list_make_ptr_cell(x1), list_make_ptr_cell(x2), \
                    list_make_ptr_cell(x3), list_make_ptr_cell(x4))
#define list_make5(x1,x2,x3,x4,x5) \
    list_make5_impl(T_List, list_make_ptr_cell(x1), list_make_ptr_cell(x2), \
                    list_make_ptr_cell(x3), list_make_ptr_cell(x4), \
                    list_make_ptr_cell(x5))
 
#define list_make1_int(x1) \
    list_make1_impl(T_IntList, list_make_int_cell(x1))
#define list_make2_int(x1,x2) \
    list_make2_impl(T_IntList, list_make_int_cell(x1), list_make_int_cell(x2))
#define list_make3_int(x1,x2,x3) \
    list_make3_impl(T_IntList, list_make_int_cell(x1), list_make_int_cell(x2), \
                    list_make_int_cell(x3))
#define list_make4_int(x1,x2,x3,x4) \
    list_make4_impl(T_IntList, list_make_int_cell(x1), list_make_int_cell(x2), \
                    list_make_int_cell(x3), list_make_int_cell(x4))
#define list_make5_int(x1,x2,x3,x4,x5) \
    list_make5_impl(T_IntList, list_make_int_cell(x1), list_make_int_cell(x2), \
                    list_make_int_cell(x3), list_make_int_cell(x4), \
                    list_make_int_cell(x5))
 
#define list_make1_oid(x1) \
    list_make1_impl(T_OidList, list_make_oid_cell(x1))
#define list_make2_oid(x1,x2) \
    list_make2_impl(T_OidList, list_make_oid_cell(x1), list_make_oid_cell(x2))
#define list_make3_oid(x1,x2,x3) \
    list_make3_impl(T_OidList, list_make_oid_cell(x1), list_make_oid_cell(x2), \
                    list_make_oid_cell(x3))
#define list_make4_oid(x1,x2,x3,x4) \
    list_make4_impl(T_OidList, list_make_oid_cell(x1), list_make_oid_cell(x2), \
                    list_make_oid_cell(x3), list_make_oid_cell(x4))
#define list_make5_oid(x1,x2,x3,x4,x5) \
    list_make5_impl(T_OidList, list_make_oid_cell(x1), list_make_oid_cell(x2), \
                    list_make_oid_cell(x3), list_make_oid_cell(x4), \
                    list_make_oid_cell(x5))
 
#define list_make1_xid(x1) \
    list_make1_impl(T_XidList, list_make_xid_cell(x1))
#define list_make2_xid(x1,x2) \
    list_make2_impl(T_XidList, list_make_xid_cell(x1), list_make_xid_cell(x2))
#define list_make3_xid(x1,x2,x3) \
    list_make3_impl(T_XidList, list_make_xid_cell(x1), list_make_xid_cell(x2), \
                    list_make_xid_cell(x3))
#define list_make4_xid(x1,x2,x3,x4) \
    list_make4_impl(T_XidList, list_make_xid_cell(x1), list_make_xid_cell(x2), \
                    list_make_xid_cell(x3), list_make_xid_cell(x4))
#define list_make5_xid(x1,x2,x3,x4,x5) \
    list_make5_impl(T_XidList, list_make_xid_cell(x1), list_make_xid_cell(x2), \
                    list_make_xid_cell(x3), list_make_xid_cell(x4), \
                    list_make_xid_cell(x5))
 
/*
 * Locate the n'th cell (counting from 0) of the list.
 * It is an assertion failure if there is no such cell.
 */
static inline ListCell *
list_nth_cell(const List *list, int n)
{
    Assert(list != NIL);
    Assert(n >= 0 && n < list->length);
    return &list->elements[n];
}
 
/*
 * Return the last cell in a non-NIL List.
 */
static inline ListCell *
list_last_cell(const List *list)
{
    Assert(list != NIL);
    return &list->elements[list->length - 1];
}
 
/*
 * Return the pointer value contained in the n'th element of the
 * specified list. (List elements begin at 0.)
 */
static inline void *
list_nth(const List *list, int n)
{
    Assert(IsA(list, List));
    return lfirst(list_nth_cell(list, n));
}
 
/*
 * Return the integer value contained in the n'th element of the
 * specified list.
 */
static inline int
list_nth_int(const List *list, int n)
{
    Assert(IsA(list, IntList));
    return lfirst_int(list_nth_cell(list, n));
}
 
/*
 * Return the OID value contained in the n'th element of the specified
 * list.
 */
static inline Oid
list_nth_oid(const List *list, int n)
{
    Assert(IsA(list, OidList));
    return lfirst_oid(list_nth_cell(list, n));
}
 
#define list_nth_node(type,list,n)  castNode(type, list_nth(list, n))
 
/*
 * Get the given ListCell's index (from 0) in the given List.
 */
static inline int
list_cell_number(const List *l, const ListCell *c)
{
    Assert(c >= &l->elements[0] && c < &l->elements[l->length]);
    return c - l->elements;
}
 
/*
 * Get the address of the next cell after "c" within list "l", or NULL if none.
 */
static inline ListCell *
lnext(const List *l, const ListCell *c)
{
    Assert(c >= &l->elements[0] && c < &l->elements[l->length]);
    c++;
    if (c < &l->elements[l->length])
        return (ListCell *) c;
    else
        return NULL;
}
 
/*
 * foreach -
 *    a convenience macro for looping through a list
 *
 * "cell" must be the name of a "ListCell *" variable; it's made to point
 * to each List element in turn.  "cell" will be NULL after normal exit from
 * the loop, but an early "break" will leave it pointing at the current
 * List element.
 *
 * Beware of changing the List object while the loop is iterating.
 * The current semantics are that we examine successive list indices in
 * each iteration, so that insertion or deletion of list elements could
 * cause elements to be re-visited or skipped unexpectedly.  Previous
 * implementations of foreach() behaved differently.  However, it's safe
 * to append elements to the List (or in general, insert them after the
 * current element); such new elements are guaranteed to be visited.
 * Also, the current element of the List can be deleted, if you use
 * foreach_delete_current() to do so.  BUT: either of these actions will
 * invalidate the "cell" pointer for the remainder of the current iteration.
 */
#define foreach(cell, lst)  \
    for (ForEachState cell##__state = {(lst), 0}; \
         (cell##__state.l != NIL && \
          cell##__state.i < cell##__state.l->length) ? \
         (cell = &cell##__state.l->elements[cell##__state.i], true) : \
         (cell = NULL, false); \
         cell##__state.i++)
 
/*
 * foreach_delete_current -
 *    delete the current list element from the List associated with a
 *    surrounding foreach() or foreach_*() loop, returning the new List
 *    pointer; pass the name of the iterator variable.
 *
 * This is similar to list_delete_cell(), but it also adjusts the loop's state
 * so that no list elements will be missed.  Do not delete elements from an
 * active foreach or foreach_* loop's list in any other way!
 */
#define foreach_delete_current(lst, var_or_cell)    \
    ((List *) (var_or_cell##__state.l = list_delete_nth_cell(lst, var_or_cell##__state.i--)))
 
/*
 * foreach_current_index -
 *    get the zero-based list index of a surrounding foreach() or foreach_*()
 *    loop's current element; pass the name of the iterator variable.
 *
 * Beware of using this after foreach_delete_current(); the value will be
 * out of sync for the rest of the current loop iteration.  Anyway, since
 * you just deleted the current element, the value is pretty meaningless.
 */
#define foreach_current_index(var_or_cell)  (var_or_cell##__state.i)
 
/*
 * for_each_from -
 *    Like foreach(), but start from the N'th (zero-based) list element,
 *    not necessarily the first one.
 *
 * It's okay for N to exceed the list length, but not for it to be negative.
 *
 * The caveats for foreach() apply equally here.
 */
#define for_each_from(cell, lst, N) \
    for (ForEachState cell##__state = for_each_from_setup(lst, N); \
         (cell##__state.l != NIL && \
          cell##__state.i < cell##__state.l->length) ? \
         (cell = &cell##__state.l->elements[cell##__state.i], true) : \
         (cell = NULL, false); \
         cell##__state.i++)
 
static inline ForEachState
for_each_from_setup(const List *lst, int N)
{
    ForEachState r = {lst, N};
 
    Assert(N >= 0);
    return r;
}
 
/*
 * for_each_cell -
 *    a convenience macro which loops through a list starting from a
 *    specified cell
 *
 * The caveats for foreach() apply equally here.
 */
#define for_each_cell(cell, lst, initcell)  \
    for (ForEachState cell##__state = for_each_cell_setup(lst, initcell); \
         (cell##__state.l != NIL && \
          cell##__state.i < cell##__state.l->length) ? \
         (cell = &cell##__state.l->elements[cell##__state.i], true) : \
         (cell = NULL, false); \
         cell##__state.i++)
 
static inline ForEachState
for_each_cell_setup(const List *lst, const ListCell *initcell)
{
    ForEachState r = {lst,
    initcell ? list_cell_number(lst, initcell) : list_length(lst)};
 
    return r;
}
 
/*
 * Convenience macros that loop through a list without needing a separate
 * "ListCell *" variable.  Instead, the macros declare a locally-scoped loop
 * variable with the provided name and the appropriate type.
 *
 * Since the variable is scoped to the loop, it's not possible to detect an
 * early break by checking its value after the loop completes, as is common
 * practice.  If you need to do this, you can either use foreach() instead or
 * manually track early breaks with a separate variable declared outside of the
 * loop.
 *
 * Note that the caveats described in the comment above the foreach() macro
 * also apply to these convenience macros.
 */
#define foreach_ptr(type, var, lst) foreach_internal(type, *, var, lst, lfirst)
#define foreach_int(var, lst)   foreach_internal(int, , var, lst, lfirst_int)
#define foreach_oid(var, lst)   foreach_internal(Oid, , var, lst, lfirst_oid)
#define foreach_xid(var, lst)   foreach_internal(TransactionId, , var, lst, lfirst_xid)
 
/*
 * The internal implementation of the above macros.  Do not use directly.
 *
 * This macro actually generates two loops in order to declare two variables of
 * different types.  The outer loop only iterates once, so we expect optimizing
 * compilers will unroll it, thereby optimizing it away.
 */
#define foreach_internal(type, pointer, var, lst, func) \
    for (type pointer var = 0, pointer var##__outerloop = (type pointer) 1; \
         var##__outerloop; \
         var##__outerloop = 0) \
        for (ForEachState var##__state = {(lst), 0}; \
             (var##__state.l != NIL && \
              var##__state.i < var##__state.l->length && \
             (var = (type pointer) func(&var##__state.l->elements[var##__state.i]), true)); \
             var##__state.i++)
 
/*
 * foreach_node -
 *    The same as foreach_ptr, but asserts that the element is of the specified
 *    node type.
 */
#define foreach_node(type, var, lst) \
    for (type * var = 0, *var##__outerloop = (type *) 1; \
         var##__outerloop; \
         var##__outerloop = 0) \
        for (ForEachState var##__state = {(lst), 0}; \
             (var##__state.l != NIL && \
              var##__state.i < var##__state.l->length && \
             (var = lfirst_node(type, &var##__state.l->elements[var##__state.i]), true)); \
             var##__state.i++)
 
/*
 * 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. (But, if they
 *    are not, some callers rely on the ending cell values being separately
 *    NULL or non-NULL as defined here; don't try to optimize that.)
 *
 * The caveats for foreach() apply equally here.
 */
#define forboth(cell1, list1, cell2, list2)                         \
    for (ForBothState cell1##__state = {(list1), (list2), 0}; \
         multi_for_advance_cell(cell1, cell1##__state, l1, i), \
         multi_for_advance_cell(cell2, cell1##__state, l2, i), \
         (cell1 != NULL && cell2 != NULL); \
         cell1##__state.i++)
 
#define multi_for_advance_cell(cell, state, l, i) \
    (cell = (state.l != NIL && state.i < state.l->length) ? \
     &state.l->elements[state.i] : NULL)
 
/*
 * for_both_cell -
 *    a convenience macro which loops through two lists starting from the
 *    specified cells of each. 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, and initcell1 and initcell2 are at
 *    the same position in the respective lists.
 *
 * The caveats for foreach() apply equally here.
 */
#define for_both_cell(cell1, list1, initcell1, cell2, list2, initcell2) \
    for (ForBothCellState cell1##__state = \
             for_both_cell_setup(list1, initcell1, list2, initcell2); \
         multi_for_advance_cell(cell1, cell1##__state, l1, i1), \
         multi_for_advance_cell(cell2, cell1##__state, l2, i2), \
         (cell1 != NULL && cell2 != NULL); \
         cell1##__state.i1++, cell1##__state.i2++)
 
static inline ForBothCellState
for_both_cell_setup(const List *list1, const ListCell *initcell1,
                    const List *list2, const ListCell *initcell2)
{
    ForBothCellState r = {list1, list2,
        initcell1 ? list_cell_number(list1, initcell1) : list_length(list1),
    initcell2 ? list_cell_number(list2, initcell2) : list_length(list2)};
 
    return r;
}
 
/*
 * forthree -
 *    the same for three lists
 */
#define forthree(cell1, list1, cell2, list2, cell3, list3) \
    for (ForThreeState cell1##__state = {(list1), (list2), (list3), 0}; \
         multi_for_advance_cell(cell1, cell1##__state, l1, i), \
         multi_for_advance_cell(cell2, cell1##__state, l2, i), \
         multi_for_advance_cell(cell3, cell1##__state, l3, i), \
         (cell1 != NULL && cell2 != NULL && cell3 != NULL); \
         cell1##__state.i++)
 
/*
 * forfour -
 *    the same for four lists
 */
#define forfour(cell1, list1, cell2, list2, cell3, list3, cell4, list4) \
    for (ForFourState cell1##__state = {(list1), (list2), (list3), (list4), 0}; \
         multi_for_advance_cell(cell1, cell1##__state, l1, i), \
         multi_for_advance_cell(cell2, cell1##__state, l2, i), \
         multi_for_advance_cell(cell3, cell1##__state, l3, i), \
         multi_for_advance_cell(cell4, cell1##__state, l4, i), \
         (cell1 != NULL && cell2 != NULL && cell3 != NULL && cell4 != NULL); \
         cell1##__state.i++)
 
/*
 * forfive -
 *    the same for five lists
 */
#define forfive(cell1, list1, cell2, list2, cell3, list3, cell4, list4, cell5, list5) \
    for (ForFiveState cell1##__state = {(list1), (list2), (list3), (list4), (list5), 0}; \
         multi_for_advance_cell(cell1, cell1##__state, l1, i), \
         multi_for_advance_cell(cell2, cell1##__state, l2, i), \
         multi_for_advance_cell(cell3, cell1##__state, l3, i), \
         multi_for_advance_cell(cell4, cell1##__state, l4, i), \
         multi_for_advance_cell(cell5, cell1##__state, l5, i), \
         (cell1 != NULL && cell2 != NULL && cell3 != NULL && \
          cell4 != NULL && cell5 != NULL); \
         cell1##__state.i++)
 
/* Functions in src/backend/nodes/list.c */
 
extern List *list_make1_impl(NodeTag t, ListCell datum1);
extern List *list_make2_impl(NodeTag t, ListCell datum1, ListCell datum2);
extern List *list_make3_impl(NodeTag t, ListCell datum1, ListCell datum2,
                             ListCell datum3);
extern List *list_make4_impl(NodeTag t, ListCell datum1, ListCell datum2,
                             ListCell datum3, ListCell datum4);
extern List *list_make5_impl(NodeTag t, ListCell datum1, ListCell datum2,
                             ListCell datum3, ListCell datum4,
                             ListCell datum5);
 
pg_nodiscard extern List *lappend(List *list, void *datum);
pg_nodiscard extern List *lappend_int(List *list, int datum);
pg_nodiscard extern List *lappend_oid(List *list, Oid datum);
pg_nodiscard extern List *lappend_xid(List *list, TransactionId datum);
 
pg_nodiscard extern List *list_insert_nth(List *list, int pos, void *datum);
pg_nodiscard extern List *list_insert_nth_int(List *list, int pos, int datum);
pg_nodiscard extern List *list_insert_nth_oid(List *list, int pos, Oid datum);
 
pg_nodiscard extern List *lcons(void *datum, List *list);
pg_nodiscard extern List *lcons_int(int datum, List *list);
pg_nodiscard extern List *lcons_oid(Oid datum, List *list);
 
pg_nodiscard extern List *list_concat(List *list1, const List *list2);
pg_nodiscard extern List *list_concat_copy(const List *list1, const List *list2);
 
pg_nodiscard extern List *list_truncate(List *list, int new_size);
 
extern bool list_member(const List *list, const void *datum);
extern bool list_member_ptr(const List *list, const void *datum);
extern bool list_member_int(const List *list, int datum);
extern bool list_member_oid(const List *list, Oid datum);
extern bool list_member_xid(const List *list, TransactionId datum);
 
pg_nodiscard extern List *list_delete(List *list, void *datum);
pg_nodiscard extern List *list_delete_ptr(List *list, void *datum);
pg_nodiscard extern List *list_delete_int(List *list, int datum);
pg_nodiscard extern List *list_delete_oid(List *list, Oid datum);
pg_nodiscard extern List *list_delete_first(List *list);
pg_nodiscard extern List *list_delete_last(List *list);
pg_nodiscard extern List *list_delete_first_n(List *list, int n);
pg_nodiscard extern List *list_delete_nth_cell(List *list, int n);
pg_nodiscard extern List *list_delete_cell(List *list, ListCell *cell);
 
extern List *list_union(const List *list1, const List *list2);
extern List *list_union_ptr(const List *list1, const List *list2);
extern List *list_union_int(const List *list1, const List *list2);
extern List *list_union_oid(const List *list1, const List *list2);
 
extern List *list_intersection(const List *list1, const List *list2);
extern List *list_intersection_int(const List *list1, const List *list2);
 
/* currently, there's no need for list_intersection_ptr etc */
 
extern List *list_difference(const List *list1, const List *list2);
extern List *list_difference_ptr(const List *list1, const List *list2);
extern List *list_difference_int(const List *list1, const List *list2);
extern List *list_difference_oid(const List *list1, const List *list2);
 
pg_nodiscard extern List *list_append_unique(List *list, void *datum);
pg_nodiscard extern List *list_append_unique_ptr(List *list, void *datum);
pg_nodiscard extern List *list_append_unique_int(List *list, int datum);
pg_nodiscard extern List *list_append_unique_oid(List *list, Oid datum);
 
pg_nodiscard extern List *list_concat_unique(List *list1, const List *list2);
pg_nodiscard extern List *list_concat_unique_ptr(List *list1, const List *list2);
pg_nodiscard extern List *list_concat_unique_int(List *list1, const List *list2);
pg_nodiscard extern List *list_concat_unique_oid(List *list1, const List *list2);
 
extern void list_deduplicate_oid(List *list);
 
extern void list_free(List *list);
extern void list_free_deep(List *list);
 
pg_nodiscard extern List *list_copy(const List *oldlist);
pg_nodiscard extern List *list_copy_head(const List *oldlist, int len);
pg_nodiscard extern List *list_copy_tail(const List *oldlist, int nskip);
pg_nodiscard extern List *list_copy_deep(const List *oldlist);
 
typedef int (*list_sort_comparator) (const ListCell *a, const ListCell *b);
extern void list_sort(List *list, list_sort_comparator cmp);
 
extern int  list_int_cmp(const ListCell *p1, const ListCell *p2);
extern int  list_oid_cmp(const ListCell *p1, const ListCell *p2);
 
#endif                          /* PG_LIST_H */