Today I Learned
Today I was attempting to validate that three variables all held the same value. My clever approach was:
a = 1 b = 1 c = nil [a, b, c].uniq.one?
I expected that to return
It was returning
Showing my reasoning, elementary math style:
[a, b, c].uniq.one? # becomes => [1, 1, nil].uniq.one? # becomes => [1, nil].one?
There are two values, right?
Here’s my mistake.
In my quest for object-oriented-message-sending-purity I interpreted
one? to be about the size of the array.
But reading the docs, I’m reminded it’s not a message about the size of the array.
It’s a message that passes each item in the array to a block, and returns true if exactly one of those return values is truthy.
Without an explicit block, the implicit block is the element itself.
1 is truty.
nil is not, so yes, there is one truthy value.
What I really wanted is
[1, nil].count == 1.
In the end, I reverted to some obvious as day boolean logic of
a == b && b == c
I’m glad I wrote a test for something so small, because this particular error in this particular place would have led to a substantial security hole.
Lesson learned: just because there’s a nicely named message that sounds right doesn’t mean it’s the message I want to send. Also, quit trying to be clever.