A Constant Variable

Riddle: What’s nowhere but everywhere except where something is?

Quick blog to illustrate the power/use of my newfound favourite Ruby variable — the instance variable. Defined with an @ in front of the variable name.

For instance (pun intended):

@variable = "instance variable"

variable = "local variable"

For people new to Ruby / coding, you will be minding your business, having fun, writing methods, puts’ing “Hello World” and gets.chomp’ing responses when all of a sudden, things get complicated.

You set a value for a variable in one place / method, find you want to use it in another method, but the programme isn’t having it:

Then with a magic @ :

To successfully access / use the instance variable in different methods, note that either:

  1. it must be initialised outside of a method first (as per above example)


2. if the variable is an output of / defined in a method_A, give method_A as an argument to the method_B you’d like to use it in:

This is as opposed to calling the instance variable directly into method_B, which won’t work:

(2) can get complicated if the method does more than just return an object. So shovelling values << and using (1) comes in handy for adding to and accessing the variable from multiple methods:

Answer to riddle: Nothing

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