Difference - unless / if

Question

Can anyone explain me the difference between if and unless and when to use it?

Answer 1

The difference between if and unless is that they are exact opposites of each other:

• if takes a condition, a then-block and an optional else-block, and it evaluates the then-block if the condition is truthy, otherwise it evaluates the else-block
• unless takes a condition, a then-block and an optional else-block, and it evaluates the then-block if the condition is falsy, otherwise it evaluates the else-block

Or, in other words: they mean pretty much the same thing in Ruby as they do in English.