It occurred to me after reviewing all the feedback to my last post that despite making the connection to statement modifiers, I never directly contrasted the two. And that this might be an even simpler way of explaining the usefulness of and
/or
in Ruby. I’ve added the following examples to the original post, but in case you missed it:
and
You can think of and
is as a reversed if
statement modifier:
next if widget = widgets.pop
becomes:
next if widget = widgets.pop
Because of the low precedence of and
, no extra parentheses are needed here as they would be for &&
.
or
Likewise, or
is a reversed unless
statement modifier:
raise "Not ready!" unless ready_to_rock?
becomes:
ready_to_rock? or raise "Not ready!"
Conclusion
Which version to use – if/unless or and/or – depends on your taste and what reads well in a given case. But it’s nice to have the option.
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Of course, the if/unless and and/or relation is obvious when you know a little bit of logic:
(a and b) == ((not a) or b) and (a or b) == ((not a) and b)
Rubbish. For example, the statement “(A and B) = ((not A) or B)” is false when A is false and B is true. That is because the left-hand side if false, but the right-hand side is true.
Woops, moment of befuddlement.
((not A) or B) is equivalent implication.
What I meant to be quoting were the DeMorgan rules.
The connection make a lot more sense combined with if/unless.
(!(a ^ b)) == ((!a) v (!b))
Yup. I've been using this a bit in Amp (http://amp.carboni.ca). It's really rather handy. Whenever I use a trick like this, I try to explain it so that a newbie could use my code as a learning tool.
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