Ruby: interpolated string to variable name [duplicate]

Question

In Ruby, how can I interpolate a string to make a variable name?

I want to be able to set a variable like so:

"post_#{id}" = true

This returns a syntax error, funnily enough:

syntax error, unexpected '=', expecting keyword_end

Answer 1

I believe you can do something like:

  send("post_#{id}=", true)

That would require, of course, that you have appropriate setter/getter. Which, since you're doing this dynamically, you probably don't.

So, perhaps you could do:

  instance_variable_set("@post_#{id}",true)

To retrieve the variable:

  instance_variable_get("@post_#{id}")

BTW, if you get tired of typing instance_variable_set("@post_#{id}",true), just for fun you could do something like:

class Foo

  def dynamic_accessor(name) 
    class_eval do 
      define_method "#{name}" do
        instance_variable_get("@#{name}")
      end
      define_method "#{name}=" do |val|
        instance_variable_set("@#{name}",val)
      end
    end
  end

end

In which case you could:

2.3.1 :017 > id = 2
 => 2 
2.3.1 :018 > f = Foo.new
 => #<Foo:0x00000005436f20> 
2.3.1 :019 > f.dynamic_accessor("post_#{id}")
 => :post_2= 
2.3.1 :020 > f.send("post_#{id}=", true)
 => true 
2.3.1 :021 > f.send("post_#{id}")
 => true 
2.3.1 :022 > f.send("post_#{id}=", "bar")
 => "bar" 
2.3.1 :023 > f.send("post_#{id}")
 => "bar"