Question

how does this work?

in irb:

>> class A
>>   b = [1, 2,3]
>> end
=> [1, 2, 3]

Is b an instance variable? class variable? how would I access b from
outside the class? Is it used for meta-programming?

Answer 1

Is b an instance variable? class variable?

No, it’s a local variable inside the class ... end scope.

how would I access b from outside the class?

You wouldn’t. It goes out of scope (and is thus inaccessible) once it reaches the end.

Is it used for meta-programming?

It can be. Example:

class A
  b = [1,2,3]
  b.each do |i|
    define_method("foo#{i}") do end
  end
end

I’ve now defined the methods foo1, foo2 and foo3.

Of course this wouldn’t behave any differently if I didn’t create the variable b and just did [1,2,3].each directly. So creating a local variable by itself does nothing, it allows you to write cleaner code (the same as using local variables in a method).