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To detect and report such errors, you first
must define a class predicate, isWeight.
Most magnitudes are not weight instances, so you define isWeight
for the Magnitude class to answer false:
Magnitude method definition • instance isWeight ^ false
On the other hand, Weight instances are Weight instances, so
you define isWeight for the Weight class to answer true:
Weight method definition • instance isWeight ^ true
Thus, as you can see from the following diagram, one isWeight method
overrides the other exactly for instances of the Weight class, but not
for instances of other classes:
Object
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*-*------------*--
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Collection Magnitude <-- isWeight method answers false
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| | isWeight method answers true
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*-*-----*-- *-*-----*------------*-- |
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Bag Set Number Time Weight <-----*