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Now that you know about points, you can understand the difference between identity and equality.
Two variables with point assignments satisfy the == predicate,
and are said to have identical values, if they both refer to the same
point. In the following illustration, the second test answers
false, because the @ method produces a distinct point each
time that it is sent, and distinct points with the same x and
y values are still distinct points.
Point method definition • instance testForIdentity: aPoint Transcript show: (self == self) printString; cr; show: (self == aPoint) printString; cr. Workspace 3 @ 4 testForIdentity: 3 @ 4 Transcript true false
On the other hand, two variables with point assignments satisfy the
= predicate, and are said to have equal values, if they both refer
to points that have the same x and y values. Thus, both of
the tests answer true in the following illustration:
Point method definition • instance testForEquality: aPoint Transcript show: (self = self) printString; cr; show: (self = aPoint) printString; cr. Workspace 3 @ 4 testForEquality: 3 @ 4 Transcript true true