Question

I was experimenting with making a DSL and ran across something that confuses me. In my call method I wanted to set an initial value for @mymethod before evaulating the block. It works if I assign to the variable directly:

class Test

  class << self
    attr_accessor :mymethod
  end

  def self.call(&block)
    @mymethod="foo"
    class_eval &block
  end

end

Test.call do
  puts "mymethod returned: #{mymethod}"
  mymethod = "bar"
  puts "mymethod is now: #{mymethod}"
end

Which returns:

[1] pry(main)> load 'test.rb'
mymethod returned: foo
mymethod is now: bar
=> true

But I feel like this should work and it doesn’t. The only thing that has changed is the @ has been removed from the assignment to mymethod so I think it should be using the mymethod= method created by attr_accessor:

class Test

  class << self
    attr_accessor :mymethod
  end

  def self.call(&block)
    mymethod="foo"
    class_eval &block
  end

end

Test.call do
  puts "mymethod returned: #{mymethod}"
  mymethod = "bar"
  puts "mymethod is now: #{mymethod}"
end

However the assignment to mymethod from within call fails while the same assignment inside the block succeeds:

[1] pry(main)> load 'test.rb'
mymethod returned: 
mymethod is now: bar
=> true

What’s going on here? Can someone explain to my why the assignment would fail inside the call method?

Answer 1

in your case, mymethod="foo" will define mymethod local variable
rather than call mymethod= method.

use self.mymethod="foo" instead