From: Paul Brannan <pbrannan@...>
Date: 2007-09-23T21:49:40+09:00
Subject: returning from an iteration loop in an extension

How can I write something like this using the C API:

  def foo(container)
    container.each do |x|
      return 42
    end
  end

If I write the loop like this:

  static VALUE iter_i(VALUE sequence)
  {
    return rb_funcall(sequence, rb_intern("each"), 0);
  }

  static VALUE body_i(VALUE val, VALUE ignore)
  {
    /* What to put here? */
  }

  static VALUE foo(VALUE sequence)
  {
    rb_iterate(iter_i, sequence, body_i, Qnil);
  }

then I see no good way to pass the return value from body_i into foo.
Thus, if I write:

  class Container
    def each(&block)
      block.call(1)
      block.call(2)
      block.call(3)
      return 10
    end
  end

then the result should be 42.

Ruby sets tag->retval before executing JUMP_TAG, but I see no way to do
this with the C API.  A similar problem exists with "break".

Is it possible to do this or could the C API be modified so it's
possible to get the same behavior as in Ruby?

Thanks,

Paul