Question

For other types of variables, I use ||=, but this doesn’t work for booleans (x ||= true assigns x to true even if x was previously assigned to false).

I’d thought that this would work:

x = true unless defined?(x)

But it doesn’t: it assigns x to nil for some reason. (An explanation here would be appreciated.)

I do know one method that works:

unless defined?(x)
  x = true
end

But it’s rather verbose. Is there a more concise way to assign default values to boolean variables in Ruby?

Answer 1

You must have defined? first, else the parser reaches x = and then defines x (which makes it nil) before running the unless:

defined?(x) or x = true
x  #=> true

x = false
defined?(x) or x = true
x  #=> false

Doing a if/unless block (instead of post-if/unless one-liner) also works:

unless defined?(x)
  x = true
end
x  #=> true

x = false
unless defined?(x)
  x = true
end
x  #=> false