In Ruby why won't `foo = true unless defined?(foo)` make the assignment?

Question

What\'s going on here? What is the subtle difference between the two forms of \"unless\"?

> irb(main):001:0> foo = true unless defined?(foo)
=> nil         


        

Answer 1

in the first instance you call foo into existence in the assignment statement. Maybe this will clarify:

bar = if true
         puts bar.class
      else
         puts "not reached"
      end
NilClass
=> nil

baz = if true
         puts baz.class
         42
      else
         puts "not reached"
      end
NilClass
=> 42