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

Well.. One form is a block and one form isn't. The second part, the block, returns the last statement evaluated. The first one.. Hrm.. I don't know exactly what it's doing.