Re: [QUIZ] Modular Arithmetic (#179)


Just a preview of my solution (inspired by TZFile):

Mod26=ModularBase.new(26)
Mod8=ModularBase.new(8)

def test_incompat_bases
assert_raises(ArgumentError) do
Mod26.new(1)+Mod8.new(1)
end
assert_nothing_raised do
Mod26.new(1)+Mod8.new(1).to_i
end
end

That said, please clarify on the behavior of a couple tests:

#new
def test_add_reverse
a = Mod26.new(15)
assert_equal(???, 15 + a)
end

#new
def test_sub_reverse
a = Mod26.new(15)
assert_equal(???, 1-a)
end

#already defined
def test_mul_int_reverse
a = Mod8.new(15)
assert_equal(77, 11 * a)
end

Clearly a Modulo +/*/- an Integer should give a Modulo
Should the reverse relation promote the Modulo to an Integer, or
promote
the Integer to a Modulo (of the same base)?


This issue requires some sort of design decision, which I
intentionally left out of the requirements, so you may do what you
like in this respect, and perhaps explain why you made a particular
choice.

When I started experimenting with my own solution, my design choice
was that the result type of any operation was the same as the first
operand. I did this primarily for simplicity, since I didn't need to
raise errors for incompatible bases, and most operations became
trivial. Of course, this choice is not without problem, since some
operations that might normally be communitive (if compatible modulo
was enforced) are no longer communitive.

In context with your questions above and my particular design choice:

1. I didn't raise any errors for mismatched bases; I used the left
operand to determine the result's type.
2. As all your reverse tests (which should be considered by all
implementors) have a left Integer argument, all the answers would be
the same, and the domain would be the full integer set. So, from top
to bottom, I would replace ??? with 30 and -14.



.

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