How to check if a variable exists with a value without "undefined local variable or method"?

exists, ruby, ruby-on-rails, undefined, variables

Solution

Change the `present?` to `!= ''` and use the && operator which only tries to evaluate the seond expression if the first one is true:

if defined?(mmm) && (mmm != '') then puts "yes" end

But actually as of 2019 this is no longer needed as both the below work

irb(main):001:0> if (defined? mm) then
irb(main):002:1* if mm.present? then
irb(main):003:2* p true
irb(main):004:2> end
irb(main):005:1> end
=> nil
irb(main):006:0> if (defined? mm) then
irb(main):007:1* p mm
irb(main):008:1> end
=> nil

Problem

This is a common pattern: If a variable doesn't exist I get an `undefined local variable or method` error. The existing code has `if variable_name.present?` but this didn't account for the variable not existing. How can I check the value of the variable and also account for it not existing at all? I've tried: ``` if (defined? mmm) then if mmm.present? then puts "true" end end ``` but Ruby still checks that inner `mmm.present?` and throws "no such variable" when it doesn't exist. I'm sure there's a common pattern/solution to this.

Original source