CODEWITHSUNDEEP
rubyif-statementsyntax
ChrisP
ChrisP

Reputation: 137

Understanding Calling Variables in Ruby

I'm trying to understand what's happening here in this short little snippet, but I'm not well versed in Ruby. Ultimately, what I'm trying to figure out is what's the difference between .path and [:path]?

if(hit.props && hit.props.path)
      original_path = hit.props[:path]

I understand the if-statement part. Check if hit has props, and if it does check to see if it also has path in the props. I'm just confused as to what [:path] is trying to accomplish.

Upvotes: 0

Views: 48

Answers (1)

Schwern
Schwern

Reputation: 165576

what's the difference between .path and [:path]

.path is a method call. :path creates a Symbol.

hit.props.path calls the props method on the hit object. Then calls .path on whatever is returned from that. It's equivalent to:

tmp = hit.props
tmp.path

hit.props[:path] again calls the props method on the hit object. Then fetches the value from that (which is probably a Hash) the :path key. :path is a Symbol which is kind of like a read-only shared String. They're often used as hash keys to save a bit of memory and to make things look a bit neater.

It's equivalent to:

tmp = hit.props
val = tmp[:path]

While I said Symbols are similar to Strings, they are not Strings. tmp[:path] and tmp["path"] are not equivalent.

What your code is doing is checking that hit.props and hit.props.path exist before trying hit.props[:path]. This is probably incorrect; hit.props.path is not used.

You probably only want to check for hit.props before trying to use it as a Hash.

if hit.props
  original_path = hit.props[:path]

This can be further reduced using the Safe Navigation Operator &. introduced in Ruby 2.3.

original_path = hit.props&.[](:path)

It works just like a normal method call, but if the object is nil the call will return nil rather than an error. If hit.props is nil then original_path will be nil. It DRYs up your code and eliminates redundant method calls; hit.props is only called once.

Note that we're taking advantage of the fact that props[:path] is really syntax sugar for calling the method [] on the props object. A bit mind-bending, but all that's happening is it's a method with a weird name.

Upvotes: 3

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