How to access instance variable from a block

Question

I have a pretty lame question regarding ruby. I have a following code:

@node          = Node.find(params[:id])
@similar_nodes = Tire.search 'nodes', load: true do
  query do
    fuzzy_like_this @node.title
  end
end

The problem is, that, for some reason, i can't access @node variable in fuzzy_like_this line. It returns nil even if Node has been found and i can access it in the second line. Can you please give me any advice why is that happening and what can i do to understand that behaviour better? I don't even know how to search for that.

Edit: Sorry for the typo in the title, ofcourse it should not be a "global" variable but instance variable.

Ican't see any global variables...

Arup Rakshit
– Arup Rakshit

2013-11-05 20:29:17 +00:00
Commented Nov 5, 2013 at 20:29 — Arup Rakshit
– Arup Rakshit, Commented Nov 5, 2013 at 20:29
edit added. Thanks for the tip!

mbajur
– mbajur

2013-11-05 20:35:28 +00:00
Commented Nov 5, 2013 at 20:35 — mbajur
– mbajur, Commented Nov 5, 2013 at 20:35

crazymykl · Accepted Answer · 2013-11-05 20:31:31Z

2

Node is an instance variable, not a global. Since the block may be (in this case, is) executed in the context of another object, your ivars aren't there. Assigning the ivar value to a local name should work, as locals are lexically scoped.

tl;dr: node = @node, use local node within block.

answered Nov 5, 2013 at 20:31

crazymykl

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1 Comment

Arup Rakshit Over a year ago

Yes.. This is the exact reason.. Good catch!

Renato Zannon · Accepted Answer · 2013-11-05 20:32:15Z

Variables starting with '@' aren't global; they are instance variables. This means that they belong to a particular object, being (mostly) inaccessible from others.

What seems to be happening is that the search method is changing the context of execution (probably via instance_eval/instance_exec), which means that, inside the block, your self isn't the same, and you won't have access to the same instance variables.

A simple workaround is to use a local variable instead:

node           = Node.find(params[:id])
@similar_nodes = Tire.search 'nodes', load: true do
  query do
    fuzzy_like_this node.title
  end
end

Then, if you really need node to be an instance variable, you can assign it later:

@node = node

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