Ruby: using .send within a method behaves differently than calling it outside

Question

I'm trying to write a little snippet for my Rails app that checks if any tags are present for an object.

I have the following code:

def any_tags_present?(obj,*tags)
  tags ||= %w(person city country other)
  tags.any? { |tag| obj.send("#{tag}_list").present? }
end

running tags.any? { |tag| obj.send("#{tag}_list").present? } will return true if I call it directly:

obj = Article.first
tags ||= %w(person city country other)
tags.any? { |tag| obj.send("#{tag}_list").present? }

=> true

but if I call it with any_tags_present?(Article.first) I get false:

obj = Article.first
any_tags_present?(obj)

=> false

What gives?

Answer 1

You can something like

def any_tags_present?(obj, tags=nil)
  tags ||= %w(person city country other)
  tags.any? { |tag| obj.send("#{tag}_list").present? }
end

obj = Article.first
any_tags_present?(obj)

So if you don't pass tags then it gets initialized by %w(person city country other)

Answer 2

The problem is the line tags ||= %w(person city country other). It doesn't get (re)assigned, because tags will be an empty Array ([]) and not nil. Possible solutions are just taking an default argument of nil and passing in an Array or checking if tags is empty.