Today we’re going to discuss a couple of really simple numeric predicates - namely Numeric#zero? and Numeric#nonzero?. I assume most Ruby developers are familiar with them, as they represent a popular alternative to doing traditional checks for zero:

if foo == 0 ...

if ...

if foo != 0 ...

if foo.nonzero? ...

So far, so good. Nothing really weird, right? Let’s now take a closer at the two predicate methods:
# => true
#=> nil
#=> false
#=> 1

Now this looks kind of weird… As you can see zero? returns true or false and nonzero? returns its receiver or nil. So much for API symmetry. There’s a long weird story behind this inconsistency, and an interesting ticket on Ruby’s bug tracker discussing options how to address it. Most of the time you probably won’t experience any issues related to that inconsistency, but there are certainly cases where it is going to bite you.1

As far as I’m concerned nonzero? doesn’t exist and I simply use !zero? all the time. Negative predicates are pretty weird in the first place and I’ve never seen much value in them.2

I’ll end this post with a small challenge for you - what are your favourite examples of API inconsistency in Ruby?

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