Local Variables vs.Instance Variables in Rails?

Question

While this topic has been covered in the past (local variables vs. instance variables), I was hoping for a bit of help. I've read all sorts of documentation on this subject and while I loosely understand that a local variable exists within a block and an instance variable can be called on and used by other methods, I was hoping to get more clarity from the community.

Can any of you be so kind as to explain what a local variable is vs. and instance variable in the context of an example? Possibly a user story? I'd prefer not to see any code, rather see a story then write code around that story as an exercise. Example; "here is the story of a local variable; Jane goes to the store..." Or, "here's the story of an instance variable, Bill goes to the store..." etc.

I see a lot of other folks are struggling with this, so I am guessing that two quality stories should go A LONG way in helping LOTS of noooobs like me.

Thanks!!!

pjammer · Accepted Answer · 2012-09-21 00:12:06Z

2

Have you been to an amusement park?

If you buy an all you can ride pass, you can go on all the rides, like rollercoasters, ferris wheels and the dirt bike course.

All instance variables are your @pass, because in ruby the instance variable starts with the @ sign.

Local variables are like only having access to one section of the ride areas. Your pass is just good for the ferris wheel. Once you are outside the ferris wheel section, no one cares about the pass any more and asks, wtf is this!

In ruby terms, variables are assigned and used in scopes, and if you need to go to other scopes, or methods, you use those instance variables to continue the fun there.

answered Sep 21, 2012 at 0:12

pjammer

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Michael Durrant · Accepted Answer · 2012-09-20 21:31:02Z

1

A dairy uses a template (Model/Class) to print milk cartons Jane goes to the store and buys milk. She now has an instance of a milk (container).

That milk container has had a sticker added to it that says "use today".

You won't see that sticker on the model used for making the container.
You won't see that sticker on each instance of the model.
You'll only see that sticker at your local store when they put it on at 5pm for that specific carton that is about to expire.

This is not exactly what local variable means but it's one "sort-of" analogy for the real world.

answered Sep 20, 2012 at 21:31

Michael Durrant

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