Using structs in Ruby on Rails gives dynamic constant assignment (SyntaxError)

Question

In my controller I have the following simplified code:

def index   @dashboard_items = []   DashItem = Struct.new(:name, :amount, :moderated)  # Error is here    [:page, :post].each do |c|     obj = c.to_s.capitalize.constantize     @dashboard_items << DashItem.new(c.to_s, obj.count, obj.count_moderated)   end end 

But Ruby gives the following error:

dynamic constant assignment (SyntaxError)

on the line marked above.

Which, AFAIK, means that the constant DashItem is already defined. Is this correct? And what to do about it?

Answer 1

The error explains what the problem is - you have a constant being assigned in a context that's too dynamic - i.e. inside the index method.

The solution is to define it outside:

DashItem = Struct.new(:name, :amount, :moderated) def index   @dashboard_items = []   ... 

Answer 2

If you want to keep the whole thing neatly inside your index method you could do this:

def index   @dashboard_items = []   # Set the name of your struct class as the first argument   Struct.new('DashItem', :name, :amount, :moderated)   ...   # Then when you want to create an instance of your structure   # you can access your class within the Struct class   @dashboard_items << Struct::DashItem.new(c.to_s, obj.count, obj.moderated) end 

As gunn said, you just can't explicitly assign a constant within a method like that...

This solution is explained more in the ruby docs here, second example on the page.