EiffelBase class
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Eiffel Class
indexing
description: "Structures whose items may be accessed sequentially, one-way";
status: "See notice at end of class";
names: sequential, traversing;
access: membership;
contents: generic;
date: "$Date: 2007-03-30 11:10:11 -0800 (Fri, 30 Mar 2007) $";
revision: "$Revision: 95354 $"
deferred class LINEAR [G]
inherit
TRAVERSABLE [G]
feature -- Access
has (v: like item): BOOLEAN is
-- Does structure include an occurrence of v?
-- (Reference or object equality,
-- based on object_comparison.)
do
start;
if notoff then
search (v)
end;
Result := notexhausted
end;
index_of (v: like item; i: INTEGER): INTEGER is
-- Index of i-th occurrence of v.
-- 0 if none.
-- (Reference or object equality,
-- based on object_comparison.)
require
positive_occurrences: i > 0
local
occur, pos: INTEGER
do
if object_comparison then
if v /= void then
from
start;
pos := 1
until
off or else (occur = i)
loop
if item /= void and then v.is_equal (item) then
occur := occur + 1
end;
forth;
pos := pos + 1
end
end
else
from
start;
pos := 1
until
off or else (occur = i)
loop
if item = v then
occur := occur + 1
end;
forth;
pos := pos + 1
end
end;
if occur = i then
Result := pos - 1
end
ensure
non_negative_result: Result >= 0
end;
search (v: like item) is
-- Move to first position (at or after current
-- position) where item and v are equal.
-- (Reference or object equality,
-- based on object_comparison.)
-- If no such position ensure that exhausted will be true.
do
if object_comparison then
if v = void then
finish;
if notafter then
forth
end
else
from
until
exhausted or else (item /= void and then v.is_equal (item))
loop
forth
end
end
else
from
until
exhausted or else v = item
loop
forth
end
end
ensure
object_found: (notexhausted and then object_comparison and then v /= void and then item /= void) implies v.is_equal (item);
item_found: (notexhausted and notobject_comparison) implies v = item
end;
index: INTEGER is
-- Index of current position
deferred
end;
occurrences (v: G): INTEGER is
-- Number of times v appears.
-- (Reference or object equality,
-- based on object_comparison.)
do
from
start;
search (v)
until
exhausted
loop
Result := Result + 1;
forth;
search (v)
end
end;
feature -- Status report
exhausted: BOOLEAN is
-- Has structure been completely explored?
do
Result := off
ensure
exhausted_when_off: off implies Result
end;
after: BOOLEAN is
-- Is there no valid position to the right of current one?
deferred
end;
off: BOOLEAN is
-- Is there no current item?
do
Result := empty or after
end;
feature -- Cursor movement
finish is
-- Move to last position.
deferred
end;
forth is
-- Move to next position; if no next position,
-- ensure that exhausted will be true.
require
not_after: notafter
deferred
end;
feature -- Conversion
linear_representation: LINEAR [G] is
-- Representation as a linear structure
do
Result := Current
end;
invariant
after_constraint: after implies off;
end -- class LINEAR
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