Class DS_LIST_CURSOR

note

description:

    "Cursors for list traversals"

library:    "Gobo Eiffel Structure Library"
author:     "Eric Bezault <ericb@gobosoft.com>"
copyright:  "Copyright (c) 1999, Eric Bezault and others"
license:    "MIT License"

deferred class interface

DS_LIST_CURSOR [G]

inherit

DS_BILINEAR_CURSOR [G]
    DS_LINEAR_CURSOR [G]
        DS_CURSOR [G]
DS_DYNAMIC_CURSOR [G]
    DS_CURSOR [G]
DS_INDEXED_CURSOR [G]
    DS_CURSOR [G]

feature -- Access

item: G
        -- Item at cursor position
        -- (From DS_CURSOR.)
    require
        not_off: not off
    deferred

index: INTEGER
        -- Index of current position
        -- (From DS_INDEXED_CURSOR.)
    deferred
    ensure
        valid_index: valid_index (Result)

container: DS_LIST [G]
        -- List traversed
        -- (From DS_CURSOR.)
    deferred

feature -- Status report

is_first: BOOLEAN
        -- Is cursor on first item?
        -- (From DS_LINEAR_CURSOR.)
    deferred
    ensure
        not_empty: Result implies not container.is_empty
        not_off: Result implies not off
        definition: Result implies (item = container.first)

is_last: BOOLEAN
        -- Is cursor on last item?
        -- (From DS_BILINEAR_CURSOR.)
    deferred
    ensure
        not_empty: Result implies not container.is_empty
        not_off: Result implies not off
        definition: Result implies (item = container.last)

after: BOOLEAN
        -- Is there no valid position to right of cursor?
        -- (From DS_LINEAR_CURSOR.)
    deferred

before: BOOLEAN
        -- Is there no valid position to left of cursor?
        -- (From DS_BILINEAR_CURSOR.)
    deferred

off: BOOLEAN
        -- Is there no item at cursor position?
        -- (From DS_CURSOR.)

same_position (other: like Current): BOOLEAN
        -- Is current cursor at same position as other?
        -- (From DS_CURSOR.)
    require
        other_not_void: other /= Void
    deferred

valid_index (i: INTEGER): BOOLEAN
        -- Is i a valid index value?
        -- (From DS_INDEXED_CURSOR.)
    ensure
        definition: Result = (0 <= i and i <= (container.count + 1))

feature -- Cursor movement

start
        -- Move cursor to first position.
        -- (From DS_LINEAR_CURSOR.)
    deferred
    ensure
        empty_behavior: container.is_empty implies after
        not_empty_behavior: not container.is_empty implies is_first

finish
        -- Move cursor to last position.
        -- (From DS_BILINEAR_CURSOR.)
    deferred
    ensure
        empty_behavior: container.is_empty implies before
        not_empty_behavior: not container.is_empty implies is_last

forth
        -- Move cursor to next position.
        -- (From DS_LINEAR_CURSOR.)
    require
        not_after: not after
    deferred

back
        -- Move cursor to previous position.
        -- (From DS_BILINEAR_CURSOR.)
    require
        not_before: not before
    deferred

search_forth (v: G)
        -- Move to first position at or after current
        -- position where item and v are equal.
        -- (Use equality_tester's criterion from container
        -- if not void, use `=' criterion otherwise.)
        -- Move after if not found.
        -- (From DS_LINEAR_CURSOR.)
    require
        not_off: not off or after
    deferred

search_back (v: G)
        -- Move to first position at or before current
        -- position where item and v are equal.
        -- (Use equality_tester's criterion from container
        -- if not void, use `=' criterion otherwise.)
        -- Move before if not found.
        -- (From DS_BILINEAR_CURSOR.)
    require
        not_off: not off or before
    deferred

go_after
        -- Move cursor to after position.
        -- (From DS_LINEAR_CURSOR.)
    deferred
    ensure
        after: after

go_before
        -- Move cursor to before position.
        -- (From DS_BILINEAR_CURSOR.)
    deferred
    ensure
        before: before

go_to (other: like Current)
        -- Move cursor to other's position.
        -- (From DS_CURSOR.)
    require
        other_not_void: other /= Void
        valid_cursor: container.valid_cursor (other)
    deferred
    ensure
        same_position: same_position (other)

go_i_th (i: INTEGER)
        -- Move cursor to i-th position.
        -- (From DS_INDEXED_CURSOR.)
    require
        valid_index: valid_index (i)
    deferred
    ensure
        moved: index = i

feature -- Comparison

is_equal (other: like Current): BOOLEAN
        -- Are other and current cursor at the same position?
        -- (From GENERAL.)
    require
        other_not_void: other /= Void
    ensure
        consistent: standard_is_equal (other) implies Result
        same_type: Result implies same_type (other)
        symmetric: Result implies other.is_equal (Current)

feature -- Duplication

copy (other: like Current)
        -- Copy other to current cursor.
        -- (From GENERAL.)
    require
        other_not_void: other /= Void
        type_identity: same_type (other)
    ensure
        is_equal: is_equal (other)

feature -- Element change

put_left (v: G)
        -- Add v to left of cursor position.
        -- Do not move cursors.
    require
        extendible: container.extendible (1)
        not_before: not before
    ensure
        one_more: container.count = old (container.count) + 1

put_right (v: G)
        -- Add v to right of cursor position.
        -- Do not move cursors.
    require
        extendible: container.extendible (1)
        not_after: not after
    ensure
        one_more: container.count = old (container.count) + 1

force_left (v: G)
        -- Add v to left of cursor position.
        -- Do not move cursors.
    require
        not_before: not before
    ensure
        one_more: container.count = old (container.count) + 1

force_right (v: G)
        -- Add v to right of cursor position.
        -- Do not move cursors.
    require
        not_after: not after
    ensure
        one_more: container.count = old (container.count) + 1

replace (v: G)
        -- Replace item at cursor position by v.
        -- (From DS_DYNAMIC_CURSOR.)
    require
        not_off: not off
    deferred
    ensure
        replaced: item = v

swap (other: DS_DYNAMIC_CURSOR [G])
        -- Exchange items at current and other's positions.
        -- Note: cursors may reference two different containers.
        -- (From DS_DYNAMIC_CURSOR.)
    require
        not_off: not off
        other_not_void: other /= Void
        other_not_off: not other.off
    ensure
        new_item: item = old (other.item)
        new_other: other.item = old item

extend_left (other: DS_LINEAR [G])
        -- Add items of other to left of cursor position.
        -- Keep items of other in the same order.
        -- Do not move cursors.
    require
        other_not_void: other /= Void
        extendible: container.extendible (other.count)
        not_before: not before
    ensure
        new_count: container.count = old (container.count) + other.count

extend_right (other: DS_LINEAR [G])
        -- Add items of other to right of cursor position.
        -- Keep items of other in the same order.
        -- Do not move cursors.
    require
        other_not_void: other /= Void
        extendible: container.extendible (other.count)
        not_after: not after
    ensure
        new_count: container.count = old (container.count) + other.count

append_left (other: DS_LINEAR [G])
        -- Add items of other to left of cursor position.
        -- Keep items of other in the same order.
        -- Do not move cursors.
    require
        other_not_void: other /= Void
        not_before: not before
    ensure
        new_count: container.count = old (container.count) + other.count

append_right (other: DS_LINEAR [G])
        -- Add items of other to right of cursor position.
        -- Keep items of other in the same order.
        -- Do not move cursors.
    require
        other_not_void: other /= Void
        not_after: not after
    ensure
        new_count: container.count = old (container.count) + other.count

feature -- Removal

remove
        -- Remove item at cursor position.
        -- Move any cursors at this position forth.
    require
        not_off: not off
    ensure
        one_less: container.count = old (container.count) - 1

remove_left
        -- Remove item to left of cursor position.
        -- Move any cursors at this position forth.
    require
        not_empty: not container.is_empty
        not_before: not before
        not_first: not is_first
    ensure
        one_less: container.count = old (container.count) - 1

remove_right
        -- Remove item to right of cursor position.
        -- Move any cursors at this position forth.
    require
        not_empty: not container.is_empty
        not_after: not after
        not_last: not is_last
    ensure
        one_less: container.count = old (container.count) - 1

prune_left (n: INTEGER)
        -- Remove n items to left of cursor position.
        -- Move all cursors off.
    require
        valid_n: 0 <= n and n < index
    ensure
        new_count: container.count = old (container.count) - n

prune_right (n: INTEGER)
        -- Remove n items to right of cursor position.
        -- Move all cursors off.
    require
        valid_n: 0 <= n and n <= (container.count - index)
    ensure
        new_count: container.count = old (container.count) - n

invariant

container_not_void: container /= Void
empty_constraint: container.is_empty implies off
    -- (From DS_CURSOR.)

after_constraint: after implies off
    -- (From DS_LINEAR_CURSOR.)

not_both: not (after and before)
before_constraint: before implies off
    -- (From DS_BILINEAR_CURSOR.)

end -- class DS_LIST_CURSOR

Copyright © 1999, Eric Bezault mailto:ericb@gobosoft.com http://www.gobosoft.com Last Updated: 31 July 1999