/**

@page release_notes Release Notes

Release 7.0 (XYZ 2017)
======================

- Removals
 - Remove requester.h, monitor.h, and destroyable.h..  Migrated to the pvAccessCPP module.
 - Previously deprecated monitorPlugin.h is removed.
 - Remove pv/messageQueue.h and epics::pvData::MessageQueue
- Deprecate the following utility classes, to be removed in 8.0.
 - epics::pvData::Queue
 - epics::pvData::Executor
 - epics::pvData::TimeFunction
- Additions
 - Add pv/pvdVersion.h which is included by pv/pvIntrospect.h
 - Add epics::pvData::createRequest() function.  Alternative to epics::pvData::CreateRequest class which throws on error.
 - epics::pvData::FieldBuilder allow Structure defintion to be changed/appended
 - Add epics::pvData::ValueBuilder like FieldBuilder also sets initial values.
  - Can also be constructed using an existing PVStructure to allow "editing".
 - Add debugPtr.h wrapper with reference tracking to assist in troubleshooting shared_ptr related ref. loops.
 - Add @ref pvjson utilities

Release 6.0 (Aug. 2016)
=======================

Release 5.0 (Sep. 2015)
=======================

The main changes since release 4.0 are:

- Deprecated getXXXField() methods have been removed from PVStructure
- Convert copy methods and equals operators (re)moved
- Convert::copyUnion now always copies between subfields.
- New method getSubFieldT, like getSubField except it throws an exception
- findSubField method removed from PVStructure
- New stream operators for Field and PVField are provided
- New template versions of Structure::getField
- Fixes for static initialisation order issues
- CreateRequest prevents a possible SEGFAULT


Deprecated getXXXField methods have been removed from PVStructure
-------------------------------------------------------------------

The following methods have been removed from PVStructure

- getBooleanField
- getByteField, getShortField, getIntField, getLongField
- getUByteField, getUShortField, getUIntField, getULongField
- getStringField
- getStructureField, getUnionField
- getScalarArrayField, getStructureArrayField, getUnionArrayField

Use template getSubField instead, e.g. use

    getSubField< PVInt >(fieldName)

in place of

    getIntField(fieldName)


Convert copy methods and equals operators
-----------------------------------------

Convert copy methods where moved and replaced with methods
on PVField classes, i.e.

    PVField::copy(const PVField& from)

Methods

    PVField::copyUnchecked(const PVField& from)

were added to allow unchecked copies, to gain performance
where checked are not needed (anymore).

In addition:
- isCompatibleXXX methods were removed in favour of Field::operator==.
- equals methods were remove in favour of PVField::operator==.
- operator== methods where moved to pvIntrospect.h and pvData.h


Convert::copyUnion
-----------------

Before this method, depending on types for to and from,
sometimes did a shallow copy, i.e. just made to shared_ptr for to 
share the same data as from.
Now it always copies between the subfield of to and from.


New method getSubFieldT, like getSubField except it throws an exception
--------------------

PVStructure has a new template member

    getSubFieldT(std::string const &fieldName)

that is like <b>getSubField</b> except that it throws a runtime_error
instead of returning null.


findSubField method removed from PVStructure
--------------------------------------------

This was mainly used in the implementation of getSubField. With a change to
the latter, findSubField was removed.


New stream operators
--------------------

New steam operators are available for Field and PVField.
Before to print a Field (or any extension) or a PVField (or any extension)
it was necessary to have code like:

     void print(StructureConstPtr struc, PVStructurePtr pv)
     {
         if(struc) {
             cout << *struc << endl;
         } else {
             cout << "nullptr\n"
         }
         if(pv) {
             cout << *.struc << endl;
         } else {
             cout << "nullptr\n"
         }
     }

Now it can be done as follows:

     void print(StructureConstPtr struc, PVStructurePtr pv)
     {
         cout << struc << endl;
         cout << pv << endl;
     }


New template version of Structure::getField
--------------------------------------------

A new template getField method has been added to Structure

template<typename FT >
std::tr1::shared_ptr< const FT > getField(std::string const &fieldName) const 

Can be used, for example, as follows:

    StructurePtr tsStruc = struc->getField<Structure>("timeStamp");


Fixes for static initialisation order issues
--------------------------------------------

Certain static builds (in particular Windows builds) of applications using
pvData had issues due to PVStructure::DEFAULT_ID being used before being initialised. This has been fixed.


CreateRequest change
--------------------

createRequest could cause a SEGFAULT if passed a bad argument.
This has been changed so the it returns a null pvStructure
and provides an error.


Release 4.0
===========

The main changes since release 3.0.2 are:

- array semantics now enforce Copy On Write.
- String no longer defined.
- timeStamp and valueAlarm name changes
- toString replaced by stream I/O 
- union is new type.
- copy is new.
- monitorPlugin is new.

New Semantics for Arrays
--------

PVScalarArray, PVStructureArray, and PVUnionArray all enforce COW (Copy On Write) Semantics.
In order to limit memory usage the storage for raw data is managed via a new shared_vector facility.
This allows multiple instances of array data to use the shared raw data.
COW is implemented via shared_vectors of const data, i. e. data that can not be modified.


String no longer defined
---------

This is replaced by std::string.


timeStamp and valueAlarm name changes
--------------

In timeStamp nanoSeconds is changed to nanoseconds.

In valueAlarm hysteresis is changed to hysteresis


toString replaced by stream I/O
---------

pvData.h and pvIntrospect no longer defines toString
Instead they have stream support.
pvIntrospect uses method dump and pvData uses dumpValue.
For example:

      PVDoublePtr pvValue;
      String buffer;
      pvValue->toString(&buffer);
      cout << buffer << endl;
      buffer.clear();
      pvValue->getField()->toString(&buffer);
      cout << buffer << evdl;

is replaced by

      PVDoublePtr pvValue;
      cout << *pvValue << endl
      cout << *pvValue->getField() << endl;


union is a new basic type.
------------

There are two new basic types: union_t and unionArray.

A union is like a structure that has a single subfield.
There are two flavors:

- *variant union* The field can have any type.
- *union* The field can any of specified set of types.

The field type can be dynamically changed.

copy 
----

This consists of createRequest and pvCopy.
createRequest was moved from pvAccess to here.
pvCopy is moved from pvDatabaseCPP and now depends
only on pvData, i.e. it no longer has any knowledge of PVRecord.

monitorPlugin
-------------

This is for is for use by code that implements pvAccess monitors.
This is prototype and is subject to debate.

Release 3.0.2
==========
This was the starting point for RELEASE_NOTES

*/