Forum: Ruby Two similar sentences have different behaviour. Is it ok?

Two similar sentences have different behaviour. Is it ok?

Compare:

1.9.3p374 :001 > a = 123 unless defined? a
 => nil
1.9.3p374 :002 > a
 => nil

but...

1.9.3p374 :003 > unless defined? b
1.9.3p374 :004?>   b = 123
1.9.3p374 :005?>   end
 => 123
1.9.3p374 :006 > b
 => 123

its because is the first sample a= is parsed first so it knows that its 
an local variable, thats why  defined? a returns true

using defined is not an good idea, showing this sample:

if false
  a = 2
end
a #=> nil