[ruby-talk:5142] Re: Types and ===

Hi,

Hal Fulton writes:
....
# First of all, I think I disagree with the assertion that the case
# statement is usually used in non-commutative situations. I think
# the most common use (this is just my first thought) is when the
# tested expression is the same type as the case limb expressions,
# in which case it becomes a simple equality test.
#
# Second of all, I think it's worth noting that the meaning of
# "receiver === other" doesn't just depend on the type of receiver,
# but also on the type of other.
#
# Therefore, isn't it conceivable that the === operator could be *made*
# to be commutative in all circumstances? It seems to me this could be
# done without violating any OOP principles.
#
# Are there any two types X and Y such that  x===y and y===x both have
# meaning, and mean different things?

Do relations like inside, outside, is-a, has-a, was-a,
could-conceivably-be-a, causes, implies, requires, subset, superset,
abbreviates, generates, extends, refines, admires, simulates, symbolizes,
and so on count as === case candidates?

Conrad Schneiker
(This note is unofficial and subject to improvement without notice.)