Yhyjyk

I am trying to write a method, that works with three types of arguments, but requires only one of them.

def convert(arg_a: 1, arg_b: 2, arg_c: 'foo')
end

Please note, that both: arg_a, and arg_b are the same type (let's say Numeric), so using one mandatory argument, and then making decision based on the input type won't work here.

At this point my code looks like this:

def convert(arg_a: nil, arg_b: nil, arg_c: nil)
 if arg_b.nil? && arg_c.nil? && arg_a
 # do something with arg_a
 elsif arg_a.nil? && arg_c.nil? && arg_b
 # do something with arg_b
 elsif arg_a.nil? && arg_b.nil? && arg_c
 # do something with arg_c
 else
 raise ArgumentError
end

In my opinion this code smells a little, and can be improved. Any thoughts?

There are lots of ways of improving this; at a high level, I'd say it's possible the method itself should be broken up into multiple methods with distinct names, because a method that accepts three different inputs and does three different things with them probably doesn't have a single responsibility.

That not withstanding, you can clean this method up by separating the argument validation from the rest of the logic. There are lots of ways of doing this, but if you just need exactly one non-nil argument, you can use something along these lines:

def convert(arg_a: nil, arg_b: nil, arg_c: nil)
 raise ArgumentError unless [arg_a, arg_b, arg_c].compact.one?

 if arg_a
 # do something with arg_a
 elsif arg_b
 # do something with arg_b
 elsif arg_c
 # do something with arg_c
 end
end

From what I can tell, your implementation only makes use of one of the three arguments, and only really expects (or allows) a single argument at a time.

i.e., with your current implementation, this is what an error-free call-site looks like:

convert(arg_a: 1)
convert(arg_b: 2)
convert(arg_c: 'foo')

If the method were called with two or more arguments (any of them), it would raise an ArgumentError, so really, this method can only be called with a single argument.

Given that you're already using keyword arguments with a default value of nil, I cannot see how this is any better than simply writing three different methods that handle the three values. Therefore, something like...

def convert_arg_a(a)
 # Handle a...
end

def convert_arg_b(b)
 # Handle b...
end

def convert_arg_c(c)
 # Handle c...
end

...should be able to do exactly what is possible with the implementation you've described, with none of the branching.