Everyone understands Boolean variables – they’re either true or they’re false. Right? Except, in languages, where the Boolean variable might be null, which makes comparing two Boolean values a little little trickier. And the DailyWTF once gave an example of a Boolean ENUM that could be true, false or file-not-found.

Long ago, when I worked for Tom Hume at Future Platforms, one of the developers suggested something more ambitious. After all, a three-state Boolean leaves too much room for ambiguity. By the time he was done, Thom Hopper had suggested 6 or 7 states for a Boolean variable. Tom Hume and I recently tried to remember as many as we could, but only got 5 or 6.

We tweeted Thom Hopper to see if he remembered, but the states of this variable are lost in time, like tears in rain. But, for the sake of posterity, I want to record some of the values that a proper Boolean type might hold:

• true
• false (obviously)
• null
• uninitialised (similar null – but this means a true/false has never been set)
• unknown (we’re currently not certain of the value)
• indeterminate (there’s no way of knowing this value)

I’ve love to be able to declare that this is stupid, but I don’t know. I mean, if you accept null as a Boolean state, where do you stop? Maybe Java needs a ‘true’ boolean that can take all of these states?