| Any values can be dynamically interpreted (traversed) and constructed through DynAny objects.
A DynAny object is associated with a data value which corresponds to a copy of the value
inserted into an any.
A DynAny object may be viewed as an ordered collection of component DynAnys.
For DynAnys representing a basic type, such as long, or a type without components,
such as an empty exception, the ordered collection of components is empty.
Each DynAny object maintains the notion of a current position into its collection
of component DynAnys. The current position is identified by an index value that runs
from 0 to n-1, where n is the number of components.
The special index value -1 indicates a current position that points nowhere.
For values that cannot have a current position (such as an empty exception),
the index value is fixed at -1.
If a DynAny is initialized with a value that has components, the index is initialized to 0.
After creation of an uninitialized DynAny (that is, a DynAny that has no value but a TypeCode
that permits components), the current position depends on the type of value represented by
the DynAny. (The current position is set to 0 or -1, depending on whether the new DynAny
gets default values for its components.)
The iteration operations rewind, seek, and next can be used to change the current position
and the current_component operation returns the component at the current position.
The component_count operation returns the number of components of a DynAny.
Collectively, these operations enable iteration over the components of a DynAny, for example,
to (recursively) examine its contents.
A constructed DynAny object is a DynAny object associated with a constructed type.
There is a different interface, inheriting from the DynAny interface, associated with
each kind of constructed type in IDL (fixed, enum, struct, sequence, union, array,
exception, and value type).
A constructed DynAny object exports operations that enable the creation of new DynAny objects,
each of them associated with a component of the constructed data value.
As an example, a DynStruct is associated with a struct value. This means that the DynStruct
may be seen as owning an ordered collection of components, one for each structure member.
The DynStruct object exports operations that enable the creation of new DynAny objects,
each of them associated with a member of the struct.
If a DynAny object has been obtained from another (constructed) DynAny object,
such as a DynAny representing a structure member that was created from a DynStruct,
the member DynAny is logically contained in the DynStruct.
Calling an insert or get operation leaves the current position unchanged.
Destroying a top-level DynAny object (one that was not obtained as a component of another DynAny)
also destroys any component DynAny objects obtained from it.
Destroying a non-top level DynAny object does nothing.
Invoking operations on a destroyed top-level DynAny or any of its descendants raises OBJECT_NOT_EXIST.
If the programmer wants to destroy a DynAny object but still wants to manipulate some component
of the data value associated with it, then he or she should first create a DynAny for the component
and, after that, make a copy of the created DynAny object.
The behavior of DynAny objects has been defined in order to enable efficient implementations
in terms of allocated memory space and speed of access. DynAny objects are intended to be used
for traversing values extracted from anys or constructing values of anys at runtime.
Their use for other purposes is not recommended.
Insert and get operations are necessary to handle basic DynAny objects
but are also helpful to handle constructed DynAny objects.
Inserting a basic data type value into a constructed DynAny object
implies initializing the current component of the constructed data value
associated with the DynAny object. For example, invoking insert_boolean on a
DynStruct implies inserting a boolean data value at the current position
of the associated struct data value.
A type is consistent for inserting or extracting a value if its TypeCode is equivalent to
the TypeCode contained in the DynAny or, if the DynAny has components, is equivalent to the TypeCode
of the DynAny at the current position.
DynAny and DynAnyFactory objects are intended to be local to the process in which they are
created and used. This means that references to DynAny and DynAnyFactory objects cannot be exported
to other processes, or externalized with ORB.object_to_string().
If any attempt is made to do so, the offending operation will raise a MARSHAL system exception.
Since their interfaces are specified in IDL, DynAny objects export operations defined in the standard
org.omg.CORBA.Object interface. However, any attempt to invoke operations exported through the Object
interface may raise the standard NO_IMPLEMENT exception.
An attempt to use a DynAny object with the DII may raise the NO_IMPLEMENT exception. |
