1SmartSolution Blog:: Entry - Finding something new where you never thought you will

Finding something new where you never thought you will

Posted At : Nov 13, 2008 19:11 PM | Posted By : Ed Tabara
Related Categories: ColdFusion

Did you know there exist an IMP operator in ColdFusion? Well, i didn't even after 8 years of day to day ColdFusion usage.
Found it accidentally when trying to have a variable name IMP.
For thouse who find IMP new too, here is how it work:

If the joiner is IMP and the first clause is false, the entire statement is true and the second will never run.

As opposite to AND and OR:

If the joiner is AND and the first clause is false, the entire statement is false and the second clause will never run.
If the joiner is OR and the first clause is true, then the entire statement is true and the second will never run.

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The same as "not x and y"

# Posted By ike | Nov 13, 2008 19:29 PM

Well. One learns something every day! In my case: two things in one day today. I looked up the docs and there's this EQV operator too. I didn't know about that either.
Cheers for the heads up.
Ike: you might want to revisit the logic of your assertion there I think: they're not the same.
Ed: your summary of how the processing of IMP is short-circuited is spot on, but it's not telling the whole picture.
If the first operand is true, then we care about the second operand, and that operand must be true for the expression to be true. If the first operand is false, the expression is true irrespective of the value of the second operator.
This is very interesting. I wonder how much of my mangled boolean contortions could have been avoided had I known about this.
Cheers!
--
Adam

# Posted By Adam Cameron | Nov 13, 2008 23:19 PM

Yeah, this is very interesting, although to be honest, I think I'd probably have used EQV more often.
So IMP works like this:
T+T = T
T+F = F
F+T = T
F+F = T
In ColdFusion, NOT x AND y is
T+T = F
T+F = F
F+T = T
F+F = F
(Remember NOT has higher precedence than AND.)
It's closer if you write NOT (x AND y):
T+T = F
T+F = T
F+T = T
F+F = T
But what you really want is NOT (x AND NOT y). And if you find yourself wanting that, then IMP would definitely be easier! (Although it might not be as understandable ... I think you'd want to comment that code.

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