5.3 Class COMPARABLE PreviousNext

indexing
description: "Objects that may be compared %
    %according to a total order relation";
note: "The basic operation is < (less than); others %
    %are defined in terms of this operation and is_equal."
deferred class interface
COMPARABLE
feature -- Comparison
infix "<" (other: like Current): BOOLEAN
        -- Is current object less than other?
    require
        other_exists: other /= Void
    deferred
    ensure
        asymmetric: Result implies not (other < Current)
infix "<=" (other: like Current): BOOLEAN
        -- Is current object less than or equal to other?
    require
        other_exists: other /= Void
    ensure
        definition: Result = (Current < other) or is_equal (other);
infix ">=" (other: like Current): BOOLEAN
        -- Is current object greater than or equal to other?
    require
        other_exists: other /= Void
    ensure
        definition: Result = (other <= Current)
infix ">" (other: like Current): BOOLEAN
        -- Is current object greater than other?
    require
        other_exists: other /= Void
    ensure
        definition: Result = (other < Current)
is_equal (other: like Current): BOOLEAN
        -- Is other attached to an object considered equal
        -- to current object?
        -- (Redefined from GENERAL.)
    require
        other_not_void: other /= Void
    ensure
        symmetric: Result implies other.is_equal (Current);
        consistent: standard_is_equal (other) implies Result;
        trichotomy: Result = (not (Current < other) and not (other < Current))
max (other: like Current): like Current
        -- The greater of current object and other
    require
        other_exists: other /= Void
    ensure
        current_if_not_smaller: (Current >= other) implies (Result = Current)
        other_if_smaller: (Current < other) implies (Result = other)
min (other: like Current): like Current
        -- The smaller of current object and other
    require
        other_exists: other /= Void
    ensure
        current_if_not_greater: (Current <= other) implies (Result = Current)
        other_if_greater: (Current > other) implies (Result = other)
three_way_comparison (other: like Current): INTEGER)
        -- If current object equal to other, 0; if smaller,
        -- -1; if greater, 1.
    require
        other_exists: other /= Void
    ensure
        equal_zero: (Result = 0) = is_equal (other);
        smaller_negative: (Result = -1) = (Current < other);
        greater_positive: (Result = 1) = (Current > other)
invariant
irreflexive_comparison: not (Current < Current)
end

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Last Updated: 26 October 1997

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