source: libcfa/src/bits/queue.hfa @ 2d0f918

#pragma once

#include "bits/collection.hfa"

// A Queue(T) is a Collection(T) defining the ordering that nodes are returned by drop() in the same order from those
// added by add(). T must be a public descendant of uColable.

// The implementation is a typical singly-linked list, except the next field of the last element points to itself
// instead of being null.

forall( T & | { T *& Next ( T * ); } ) {
        struct Queue {
                inline Collection;                                                              // Plan 9 inheritance
                T * last;                                                                               // last element, or 0 if queue is empty.
        };

        static inline {
                // wrappers to make Collection have T
                T & head( Queue(T) & q ) with( q ) {
                        return *(T *)head( (Collection &)q );
                } // post: empty() & head() == 0 | !empty() & head() in *q

                void ?{}( Queue(T) &, const Queue(T) & ) = void; // no copy
                Queue(T) & ?=?( const Queue(T) & ) = void;              // no assignment

                void ?{}( Queue(T) & q ) with( q ) {
                        ((Collection &)q){};
                        last = 0p;
                } // post: empty()

                T & tail( Queue(T) & q ) with( q ) {
                        return *last;
                }

                T * succ( Queue(T) & q, T * n ) with( q ) {             // pre: *n in *q
                        #ifdef __CFA_DEBUG__
                        if ( ! listed( n ) ) abort( "(Queue &)%p.succ( %p ) : Node is not on a list.", &q, n );
                        #endif // __CFA_DEBUG__
                        return (Next( n ) == n) ? 0p : Next( n );
                } // post: n == tail() & succ(n) == 0 | n != tail() & *succ(n) in *q

                T & addHead( Queue(T) & q, T & n ) with( q ) {
                        #ifdef __CFA_DEBUG__
                        if ( listed( &n ) ) abort( "(Queue &)%p.addHead( %p ) : Node is already on another list.", &q, &n );
                        #endif // __CFA_DEBUG__
                        if ( last ) {
                                Next( &n ) = &head( q );
                                q.root = &n;
                        } else {
                                root = last = &n;
                                Next( &n ) = &n;                                                // last node points to itself
                        }
                        return n;
                }

                T & addTail( Queue(T) & q, T & n ) with( q ) {
                        #ifdef __CFA_DEBUG__
                        if ( listed( &n ) ) abort( "(Queue &)%p.addTail( %p ) : Node is already on another list.", &q, &n );
                        #endif // __CFA_DEBUG__
                        if ( last ) Next( last ) = &n;
                        else root = &n;
                        last = &n;
                        Next( &n ) = &n;                                                        // last node points to itself
                        return n;
                }

                T & add( Queue(T) & q, T & n ) with( q ) {
                        return addTail( q, n );
                }

                T & dropHead( Queue(T) & q ) with( q ) {
                        T & t = head( q );
                        if ( root ) {
                                root = Next( (T *)root );
                                if ( &head( q ) == &t ) {
                                        root = last = 0p;                                       // only one element
                                }
                                Next( &t ) = 0p;
                        }
                        return t;
                }

                T & drop( Queue(T) & q ) with( q ) {
                        return dropHead( q );
                }

                T & remove( Queue(T) & q, T & n ) with( q ) {   // O(n)
                        #ifdef __CFA_DEBUG__
                        if ( ! listed( (Colable &)n ) ) abort( "(Queue &)%p.remove( %p ) : Node is not on a list.", &q, &n );
                        #endif // __CFA_DEBUG__
                        T * prev = 0p;
                        T * curr = (T *)root;
                        for ( ;; ) {
                                if ( &n == curr ) {                                             // found => remove
                                        if ( (T *)root == &n ) {
                                                dropHead( q );
                                        } else if ( last == &n ) {
                                                last = prev;
                                                Next( last ) = last;
                                        } else {
                                                Next( prev ) = Next( curr );
                                        }
                                        Next( &n ) = 0p;
                                        break;
                                }
                                // not found => error
                                #ifdef __CFA_DEBUG__
                                if ( curr == last ) abort( "(Queue &)%p.remove( %p ) : Node is not in list.", &q, &n );
                                #endif // __CFA_DEBUG__
                                prev = curr;
                                curr = Next( curr );
                        }
                        return n;
                } // post: ! listed( n )

                T & dropTail( Queue(T) & q ) with( q ) {                // O(n)
                        T & n = tail( q );
                        return &n ? remove( q, n ), n : *0p;
                }

                // Transfer the "from" list to the end of queue sequence; the "from" list is empty after the transfer.
                void transfer( Queue(T) & q, Queue(T) & from ) with( q ) {
                        if ( empty( from ) ) return;                            // "from" list empty ?
                        if ( empty( q ) ) {                                                     // "to" list empty ?
                                root = from.root;
                        } else {                                                                        // "to" list not empty
                                Next( last ) = &head( from );
                        }
                        last = from.last;
                        from.root = from.last = 0p;                                     // mark "from" list empty
                }

                // Transfer the "from" list up to node "n" to the end of queue list; the "from" list becomes the list after node "n".
                // Node "n" must be in the "from" list.
                void split( Queue(T) & q, Queue(T) & from, T & n ) with( q ) {
                        #ifdef __CFA_DEBUG__
                        if ( ! listed( (Colable &)n ) ) abort( "(Queue &)%p.split( %p ) : Node is not on a list.", &q, &n );
                        #endif // __CFA_DEBUG__
                        Queue(T) to;
                        to.root = from.root;                                            // start of "to" list
                        to.last = &n;                                                           // end of "to" list
                        from.root = Next( &n );                                         // start of "from" list
                        if ( &n == &head( from ) ) {                            // last node in list ?
                                from.root = from.last = 0p;                             // mark "from" list empty
                        } else {
                                Next( &n ) = &n;                                                // fix end of "to" list
                        }
                        transfer( q, to );
                }
        } // distribution
} // distribution

forall( T & | { T *& Next ( T * ); } ) {
        struct QueueIter {
                inline ColIter;                                                                 // Plan 9 inheritance
        };

        static inline {
                void ?{}( QueueIter(T) & qi ) with( qi ) {
                        ((ColIter &)qi){};
                } // post: curr == 0p

                // create an iterator active in queue q
                void ?{}( QueueIter(T) & qi, Queue(T) & q ) with( qi ) {
                        curr = &head( q );
                } // post: curr = {e in q}

                void ?{}( QueueIter(T) & qi, T & start ) with( qi ) {
                        curr = &start;
                } // post: curr = {e in q}

                // make existing iterator active in queue q
                void over( QueueIter(T) & qi, Queue(T) & q ) with( qi ) {
                        curr = &head( q );
                } // post: curr = {e in q}

                bool ?|?( QueueIter(T) & qi, T && tp ) with( qi ) {
                        if ( curr ) {
                                &tp = Curr( qi );
                                T * n = Next( Curr( qi ) );
                                curr = (n == Curr( qi ) ) ? 0p : n;
                        } else &tp = 0p;
                        return &tp != 0p;
                }
                // post: elts == null & !operator|(tp) | elts != null & *tp' in elts & elts' == elts - *tp & operator|(tp)
        } // distribution
} // distribution