code: func (v *MrbValue) GetInstanceVariable(variable string) *MrbValue {
  	cs := C.CString(variable)
  	defer C.free(unsafe.Pointer(cs))
  	return newValue(v.state, C._go_mrb_iv_get(v.state, v.value, C.mrb_intern_cstr(v.state, cs)))
  }
docs: // GetInstanceVariable gets an instance variable on this value.