Issue 16340: Fixing bugs and improving usability of the InstanceHandle<D> class (dds-psm-cxx-ftf)
Source: Real-Time Innovations (Dr. Sumant Tambe, sumant(at)rti.com)
Nature: Revision
Severity: Significant
Summary: The InstanceHandle class in dds-psm-cxx\src\hpp\tdds\core\instancehandle.hpp appears to be incomplete in several ways. 


1. A missing constructor
InstanceHandle(const DELEGATE & d) : 
dds::core::Value<DELEGATE>(d) {}


There is no way to construct an instance handle except a null one!


2. A missing copy-constructor 
InstanceHandle(const InstanceHandle& src)  : 
dds::core::Value<DELEGATE>(src.delegate()) 
{ }


3. Typos: a missing return and needs a dot instead of an arrow.


InstanceHandle& operator=(const dds::core::null_type& src) { return this->delegate().operator=(src);   }


4. Missing comparison operators to allow comparisons like 
if(dds::null == instance_handle_object) 


Currently it supports other way round. The proposed solution is to add two overloaded operators in tdds::core namespace.


template <class D>
bool operator == (dds::core::null_type, InstanceHandle<D> const &ih)
{
  return ih.is_nil();
}


template <class D>
bool operator != (dds::core::null_type, InstanceHandle<D> const &ih)
{
  return !ih.is_nil();
}


5. Finally, the InstanceHandle<D> class and in general the classes that support comparison with dds::null will benefit from supporting a generic and succinct syntax of the form: if(instance_handle_object). 


Proposed Solution:
An idiomatic way of implenting it is the safe-bool idiom, which has been used widely in standard and boost smart pointer classes, such as std::auto_ptr, boost::shared_ptr. Here is a self-sufficient file that shows one way of implementing the safe bool idiom for the instance handle class:


http://cpptruths.googlecode.com/svn/trunk/cpp/instance_handle.cpp


Other possible implementation based on the discussions on the boost mailing list is available here:

http://codepaste.net/c83uuj
Resolution: 
Revised Text: 
Actions taken:
June 20, 2011: received issue
Discussion: 

End of Annotations:=====

m: webmaster@omg.org
Date: 20 Jun 2011 00:18:58 -0400
To: <issues@omg.org>
Subject: Issue/Bug Report


*******************************************************************************
Name:            Sumant Tambe
Employer:        Real-Time Innovations
mailFrom:        sumant@rti.com
Terms_Agreement: I agree
Specification:   DDS PSM C++
Section:         7
FormalNumber:    ptc/2011-01-02
Version:         FTF Beta1
Doc_Year:        2011
Doc_Month:       January
Doc_Day:         01
Page:            4
Title:           Fixing bugs and improving usability of the InstanceHandle<D> class
Nature:          Revision
Severity:        Significant
CODE:            3TMw8
B1:              Report Issue


Description:


The InstanceHandle class in dds-psm-cxx\src\hpp\tdds\core\instancehandle.hpp appears to be incomplete in several ways. 


1. A missing constructor
InstanceHandle(const DELEGATE & d) : 
dds::core::Value<DELEGATE>(d) {}


There is no way to construct an instance handle except a null one!


2. A missing copy-constructor 
InstanceHandle(const InstanceHandle& src)  : 
dds::core::Value<DELEGATE>(src.delegate()) 
{ }


3. Typos: a missing return and needs a dot instead of an arrow.


InstanceHandle& operator=(const dds::core::null_type& src) { return this->delegate().operator=(src);   }


4. Missing comparison operators to allow comparisons like 
if(dds::null == instance_handle_object) 


Currently it supports other way round. The proposed solution is to add two overloaded operators in tdds::core namespace.


template <class D>
bool operator == (dds::core::null_type, InstanceHandle<D> const &ih)
{
  return ih.is_nil();
}


template <class D>
bool operator != (dds::core::null_type, InstanceHandle<D> const &ih)
{
  return !ih.is_nil();
}


5. Finally, the InstanceHandle<D> class and in general the classes that support comparison with dds::null will benefit from supporting a generic and succinct syntax of the form: if(instance_handle_object). 


Proposed Solution:
An idiomatic way of implenting it is the safe-bool idiom, which has been used widely in standard and boost smart pointer classes, such as std::auto_ptr, boost::shared_ptr. Here is a self-sufficient file that shows one way of implementing the safe bool idiom for the instance handle class:


http://cpptruths.googlecode.com/svn/trunk/cpp/instance_handle.cpp


Other possible implementation based on the discussions on the boost mailing list is available here:

http://codepaste.net/c83uuj