Class DS_BILINEAR

Class DS_BILINEAR_CURSOR

note

description:

    "Cursors for data structures that may be traversed forward and backward"

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_BILINEAR_CURSOR [G]

inherit

DS_LINEAR_CURSOR [G]
    DS_CURSOR [G]

feature -- Access

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

container: DS_BILINEAR [G]
        -- Data structure 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?
    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?
    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

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.
    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.
    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.
    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.
    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)

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)

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

end -- class DS_BILINEAR_CURSOR