Create multiple identical methods in Ruby

Question

In one of my models I have code like this:

def lendable_category=(i)
  set_category(i)
end

def free_category=(i)
  set_category(i)
end

def skill_category=(i)
  set_category(i)
end

The methods are virtual parameters which I've added so I can save an object using a params hash without coercing the hash in my controller.

It doesn't feel great to say the same thing three times. Is there a better way to create identical methods like this?

You could pass along an option (that apparently will not be used) do the set_category method, or you could to another method like def opt_category(i,opt) set_category(i) end, can you please explain what do you mean by 'using a params hash without coercing the hash in the controller'? — John Furtado
– John Furtado, Commented Jan 10, 2013 at 12:35
Hi John, the Rails params hash contains something like params[item:[lendable_category:"1",free_category:"",skill_category:""]]. My datamodel on the other hand only contains a category_id field. I don't want to have to parse my params hash in the controller, I'd rather have the Item model handle the different types of category join by itself. The virtual parameters let me do this, but it's not nice having to repeat the same code 3 times. — superluminary
– superluminary, Commented Jan 10, 2013 at 15:42

sailor · Accepted Answer · 2013-01-10 12:34:18Z

17

%w(lendable free skill).each do |name|
  define_method "#{name}_category" do |i|
    set_category(i)
  end
end

answered Jan 10, 2013 at 12:34

sailor

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2 Comments

superluminary Over a year ago

Brilliant. That is a relief.

the Tin Man Over a year ago

I'd also add a comment in the code saying what that is doing, because it isn't obvious, something like # defining lendable_category, free_category and skill_category. Or, use the full method names in the array, not partials. The first time someone goes to search for the method names and can't find them the comment will save the day. Sometimes completely DRYing the code can cause longer term issues by obscuring logic.

Andrew Haines · Accepted Answer · 2013-01-10 13:26:37Z

16

Alternatively, since your methods aren't doing anything other than calling set_category, you can save a couple of lines by just aliasing the method:

%w(lendable free skill).each do |name|
  alias_method "#{name}_category=", :set_category
end

answered Jan 10, 2013 at 13:26

Andrew Haines

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Comments

Josh Voigts · Accepted Answer · 2013-01-10 14:23:36Z

4

You can use the alias keyword:

alias lendable_category= set_category 
alias free_category=     set_category 
alias skill_category=    set_category

answered Jan 10, 2013 at 14:23

Josh Voigts

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1 Comment

the Tin Man Over a year ago

I prefer this over dynamically creating method names. If someone ever needed to find those method names, a quick search would locate them.

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