如何使用define_method定义？（超级）

Question

When I use define_method from within a block passed to an iterator, for some reason defined?(super) never evaluates to true .

See the example below. Note that super(value) is a valid call, even though defined? thinks otherwise.

class A
  def message=(val)
    puts 'A says ' + val
  end
end

class B < A
  ['message', 'warning'].each do |method|
    define_method(method + '=') do |val|
      puts 'B says ' + val
      super(val) if defined?(super)
    end
  end
end

a = A.new
a.message = 'hello!' # A says hello!
b = B.new
b.message = 'hello!' # B says hello!

############################################

class B < A
  ['message', 'warning'].each do |method|
    define_method(method + '=') do |val|
      puts 'B says ' + val
      super(val) rescue nil
    end
  end
end

b = B.new
b.message = 'hello!' # B says hello! A says hello!

Answer 1

This is a bug in Ruby 1.9.3 that was fixed in 2.0.0-p0 but never backported to 1.9.3. The reported bug isn't exactly the same, but its fix is likely what solved this.

Likely this arose from the fact that defined? and super are both keywords and the possible issues with scoping in a dynamic method definition via a Proc. But I'm just guessing.

You should upgrade to Ruby 2.0 (or better yet 2.1) in order to fix this—or attempt to backport the patch yourself.