Base class for classes that encapsulate SDP attributes values.

Sub-classes of this wrap specific types of SDP service record attributes. For example, CSdpBoolean derives from CSdpAttrValue to encapsulate boolean attributes. The base class defines getters for all types: for example, it declares a function Bool() that returns the attribute value as a TBool. Note though that the function would panic unless called on actual CSdpBoolean.

A common base class allows attributes of all types to be used polymorphically. You can use CSdpAttrValue's Type() function to find the actual type being used, and upcast the pointer appropriately.