Add Object#instance_exec

mrbgems/mruby-object-ext/src/object.c

 #include "mruby.h"
 #include "mruby/array.h"
+#include "mruby/class.h"
 
 /*
  *  call-seq:
@@ -40,6 +41,55 @@ nil_to_i(mrb_state *mrb, mrb_value obj)
     return mrb_fixnum_value(0);
 }
 
+/*
+ *  call-seq:
+ *     obj.instance_exec(arg...) {|var...| block }                       -> obj
+ *
+ *  Executes the given block within the context of the receiver
+ *  (_obj_). In order to set the context, the variable +self+ is set
+ *  to _obj_ while the code is executing, giving the code access to
+ *  _obj_'s instance variables.  Arguments are passed as block parameters.
+ *
+ *     class KlassWithSecret
+ *       def initialize
+ *         @secret = 99
+ *       end
+ *     end
+ *     k = KlassWithSecret.new
+ *     k.instance_exec(5) {|x| @secret+x }   #=> 104
+ */
+
+mrb_value 
+mrb_yield_internal(mrb_state *mrb, mrb_value b, int argc, mrb_value *argv, mrb_value self, struct RClass *c);
+
+static mrb_value
+mrb_obj_instance_exec(mrb_state *mrb, mrb_value self)
+{
+  mrb_value *argv;
+  int argc;
+  mrb_value blk;
+  struct RClass *c;
+  
+  mrb_get_args(mrb, "*&", &argv, &argc, &blk);
+
+  if (mrb_nil_p(blk)) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "no block given");
+  }
+
+  switch (mrb_type(self)) {
+  case MRB_TT_SYMBOL:
+  case MRB_TT_FIXNUM:
+  case MRB_TT_FLOAT:
+    c = 0;
+    break;
+  default:
+    c = mrb_class_ptr(mrb_singleton_class(mrb, self));
+    break;
+  }
+
+  return mrb_yield_internal(mrb, blk, argc, argv, self, c);
+}
+
 void
 mrb_mruby_object_ext_gem_init(mrb_state* mrb)
 {
@@ -48,6 +98,8 @@ mrb_mruby_object_ext_gem_init(mrb_state* mrb)
   mrb_define_method(mrb, n, "to_a", nil_to_a,       MRB_ARGS_NONE());
   mrb_define_method(mrb, n, "to_f", nil_to_f,       MRB_ARGS_NONE());
   mrb_define_method(mrb, n, "to_i", nil_to_i,       MRB_ARGS_NONE());
+
+  mrb_define_method(mrb, mrb->object_class, "instance_exec", mrb_obj_instance_exec, MRB_ARGS_ANY() | MRB_ARGS_BLOCK());
 }
 
 void

mrbgems/mruby-object-ext/test/object.rb

+assert('Object#instance_exec') do
+  class KlassWithSecret
+    def initialize
+      @secret = 99
+    end
+  end
+  k = KlassWithSecret.new
+  assert_equal k.instance_exec(5) {|x| @secret+x }, 104
+end