Binding.of_caller for JRuby, implemented in Ruby.

1example.txt

ext-jruby-local ~/projects/jruby $ jruby binding_of_caller.rb 
RuntimeError: caller binding only supported in interpreter
  binding_of_caller at binding_of_caller.rb:24
          of_caller at binding_of_caller.rb:4
                foo at binding_of_caller.rb:39
             (root) at binding_of_caller.rb:43

ext-jruby-local ~/projects/jruby $ jruby -X-C binding_of_caller.rb 
2

binding_of_caller.rb

class << Binding
  def of_caller(index = 1)
    index += 1 # always omit this frame
    JRuby.runtime.current_context.binding_of_caller(index)
  end
end

class org::jruby::runtime::ThreadContext
  java_import org.jruby.runtime.Binding
  java_import org.jruby.RubyBinding
  java_import org.jruby.RubyInstanceConfig::CompileMode

  field_accessor :frameStack, :frameIndex,
                 :scopeStack, :scopeIndex,
                 :backtrace, :backtraceIndex

  def binding_of_caller(index)
    index += 1 # always omit this frame

    raise IndexError, "insufficient frames for index #{index}" if index > frameIndex

    compile_mode = JRuby.runtime.instance_config.compile_mode
    unless compile_mode == CompileMode::OFF
      raise RuntimeError, "caller binding only supported in interpreter"
    end

    frame = frameStack[frameIndex - index]
    scope = scopeStack[scopeIndex - index]
    element = backtrace[backtraceIndex - index]

    binding = Binding.new(frame, scope.static_scope.module, scope, element.clone)
    JRuby.dereference(RubyBinding.new(JRuby.runtime, Binding, binding))
  end
end

x = 1

def foo
  b = Binding.of_caller
  eval "x = 2", b
end

foo
puts x

Wow, that is great!