Class DS_LINKED

Class DS_LINKED_STACK

note

description:

    "Stacks (Last-In, First-Out) implemented with linked cells"

library:    "Gobo Eiffel Structure Library"
author:     "Eric Bezault <ericb@gobosoft.com>"
copyright:  "Copyright (c) 1999-2001, Eric Bezault and others"
license:    "MIT License"

class interface

DS_LINKED_STACK [G]

inherit

DS_STACK [G]
    DS_DISPENSER [G]
        DS_SEARCHABLE [G]
            DS_CONTAINER [G]

create

make
        -- Create an empty stack.
        -- Use `=' as comparison criterion.
    ensure
        empty: is_empty

make_equal
        -- Create an empty stack.
        -- Use equal as comparison criterion.
    ensure
        empty: is_empty

make_default
        -- Create an empty stack.
        -- Use `=' as comparison criterion.
        -- (From DS_CONTAINER.)
    ensure
        empty: is_empty

feature -- Access

item: G
        -- Item at top of stack
        -- (From DS_DISPENSER.)
    require
        not_empty: not is_empty

equality_tester: DS_EQUALITY_TESTER [G]
        -- Equality tester;
        -- A void equality tester means that `='
        -- will be used as comparison criterion.
        -- (From DS_SEARCHABLE.)

feature -- Measurement

count: INTEGER
        -- Number of items in stack
        -- (From DS_CONTAINER.)

occurrences (v: G): INTEGER
        -- Number of times v appears in stack
        -- (Use equality_tester's comparison criterion
        -- if not void, use `=' criterion otherwise.)
        -- (From DS_SEARCHABLE.)
    ensure
        positive: Result >= 0
        has: has (v) implies Result >= 1

feature -- Status report

has (v: G): BOOLEAN
        -- Does stack include v?
        -- (Use equality_tester's comparison criterion
        -- if not void, use `=' criterion otherwise.)
        -- (From DS_SEARCHABLE.)
    ensure
        not_empty: Result implies not is_empty

is_empty: BOOLEAN
        -- Is stack empty?
        -- (From DS_CONTAINER.)

extendible (n: INTEGER): BOOLEAN
        -- May stack be extended with n items?
    require
        positive_n: n >= 0
    ensure
        definition: Result = True

same_items (v, u: G): BOOLEAN
        -- Are v and u considered equal?
        -- (Use equality_tester's comparison criterion
        -- if not void, use `=' criterion otherwise.)
        -- (From DS_SEARCHABLE.)

same_equality_tester (other: DS_SEARCHABLE [G]): BOOLEAN
        -- Does container use the same comparison
        -- criterion as other?
        -- (From DS_SEARCHABLE.)
    require
        other_not_void: other /= Void

equality_tester_settable (a_tester: like equality_tester): BOOLEAN
        -- Can set_equality_tester be called with a_tester
        -- as argument in current state of container?
        -- (Default answer: True.)
        -- (From DS_SEARCHABLE.)

feature -- Comparison

is_equal (other: like Current): BOOLEAN
        -- Is current stack equal to other?
        -- (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)
        same_count: Result implies count = other.count

feature -- Duplication

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

feature -- Setting

set_equality_tester (a_tester: like equality_tester)
        -- Set equality_tester to a_tester.
        -- A void equality tester means that `='
        -- will be used as comparison criterion.
        -- (From DS_SEARCHABLE.)
    require
        equality_tester_settable: equality_tester_settable (a_tester)
    ensure
        equality_tester_set: equality_tester = a_tester

feature -- Element change

put (v: G)
        -- Push v on stack.
        -- (From DS_DISPENSER.)
    require
        extendible: extendible (1)
    ensure
        one_more: count = old count + 1
        pushed: item = v

force (v: G)
        -- Push v on stack.
        -- (From DS_DISPENSER.)
    ensure
        one_more: count = old count + 1
        pushed: item = v

replace (v: G)
        -- Replace top item by v.
        -- (From DS_STACK.)
    require
        not_empty: not is_empty
    ensure
        same_count: count = old count
        replaced: item = v

extend (other: DS_LINEAR [G])
        -- Add items of other to stack.
        -- Add other.first first, etc.
        -- (From DS_DISPENSER.)
    require
        other_not_void: other /= Void
        extendible: extendible (other.count)
    ensure
        new_count: count = old count + other.count

append (other: DS_LINEAR [G])
        -- Add items of other to stack.
        -- Add other.first first, etc.
        -- (From DS_DISPENSER.)
    require
        other_not_void: other /= Void
    ensure
        new_count: count = old count + other.count

feature -- Removal

remove
        -- Remove top item from stack.
        -- (From DS_DISPENSER.)
    require
        not_empty: not is_empty
    ensure
        one_less: count = old count - 1

prune (n: INTEGER)
        -- Remove n items from stack.
        -- (From DS_DISPENSER.)
    require
        valid_n: 0 <= n and n <= count
    ensure
        new_count: count = old count - n

keep (n: INTEGER)
        -- Keep n items in stack.
        -- (From DS_DISPENSER.)
    require
        valid_n: 0 <= n and n <= count
    ensure
        new_count: count = n

wipe_out
        -- Remove all items from stack.
        -- (From DS_CONTAINER.)
    ensure
        wiped_out: is_empty

invariant

positive_count: count >= 0
empty_definition: is_empty = (count = 0)
    -- (From DS_CONTAINER.)

end -- class DS_LINKED_STACK