From: Florian Gross <flgr@...>
Date: 2004-06-12T22:23:37+09:00
Subject: Re: Any way to get the calling method's binding?

Gavin Sinclair wrote:

> Something I've wanted to do on a few occasions recently is to evaluate
> an expression in the context of the calling method.

Use this:

> begin
>   require 'simplecc'
> rescue LoadError
>   def Continuation.create(*args, &block)
>     cc = nil; result = callcc {|c| cc = c; block.call(cc) if block and args.empty?}
>     result ||= args
>     return *[cc, *result]
>   end
> end
> 
> # This method returns the binding of the method that called your
> # method. Don't use it when you're not inside a method.
> #
> # It's used like this:
> #   def inc_counter
> #     Binding.of_caller do |binding|
> #       eval("counter += 1", binding)
> #     end
> #   end
> #   counter = 0
> #   2.times { inc_counter }
> #   counter # => 2
> #
> # You will have to put the whole rest of your method into the
> # block that you pass into this method. If you don't do this
> # an Exception will be raised. Because of the way that this is
> # implemented it has to be done this way.
> def Binding.of_caller(&block)
>   old_critical = Thread.critical
>   Thread.critical = true
>   count = 0
>   cc, result, error = Continuation.create(nil, nil)
>   error.call if error
> 
>   tracer = lambda do |*args|
>     type, context = args[0], args[4]
>     if type == "return"
>       count += 1
>       # First this method and then calling one will return --
>       # the trace event of the second event gets the context
>       # of the method which called the method that called this
>       # method.
>       if count == 2
>         # It would be nice if we could restore the trace_func
>         # that was set before we swapped in our own one, but
>         # this is impossible without overloading set_trace_func
>         # in current Ruby.
>         set_trace_func(nil)
>         cc.call(eval("binding", context), nil)
>       end
>     elsif type != "line"
>       set_trace_func(nil)
>       error_msg = "Binding.of_caller used in non-method context or " +
>         "trailing statements of method using it aren't in the block."
>       cc.call(nil, lambda { raise(ArgumentError, error_msg ) })
>     end
>   end
> 
>   unless result
>     set_trace_func(tracer)
>     return nil
>   else
>     Thread.critical = old_critical
>     yield result
>   end
> end

Regards,
Florian Gross