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Basic PHP Mapping for Classes
A Slice class maps to a PHP class with the same name. For each Slice data member, the generated class contains a member variable, just as for structures and exceptions. Consider the following class definition:
The PHP mapping generates the following code for this definition:
There are a number of things to note about the generated code:
- The generated class
\Ice\Value. This reflects the semantics of Slice classes in that all classes implicitly inherit from
\Ice\Value, which is the ultimate ancestor of all classes. Note that
Valueis not the same as \
Ice\ObjectPrx. In other words, you cannot pass a class where a proxy is expected and vice versa.
- The constructor initializes an instance variable for each Slice data member.
- The class defines the method
ice_idand class method
There is quite a bit to discuss here, so we will look at each item in turn.
Value in PHP
Like interfaces, classes implicitly inherit from a common base class,
\Ice\Value. However, classes inherit from \
Ice\Value instead of \
Ice\ObjectPrx, therefore you cannot pass a class where a proxy is expected (and vice versa) because the base types for classes and proxies are not compatible.
Value defines the following functions:
These functions behave as follows:
This method returns the actual run-time type ID of the object. If you call
ice_idthrough a reference to a base instance, the returned type ID is the actual (possibly more derived) type ID of the instance.
If the object defines this method, the Ice run time invokes it just prior to marshaling the object's state, providing the opportunity for the object to validate its declared data members.
If the object defines this method, the Ice run time invokes it after unmarshaling the object's state. An object typically defines this method when it needs to perform additional initialization using the values of its declared data members.
This functions returns the
SlicedDataobject if the value has been sliced during un-marshaling or
This method is generated in each class and returns the static type ID of the class.
Class Data Members in PHP
By default, data members of classes are mapped exactly as for structures and exceptions: for each data member in the Slice definition, the generated class contains a corresponding member variable.
Optional data members use the same mapping as required data members, but an optional data member can also be set to the marker value
\Ice\Unset to indicate that the member is unset. A well-behaved program must compare an optional data member to
Unset before using the member's value:
Unset marker value has different semantics than
null is a legal value for certain Slice types, the Ice run time requires a separate marker value so that it can determine whether an optional value is set. An optional value set to
null is considered to be set. If you need to distinguish between an unset value and a value set to
null, you can do so as follows:
If you wish to restrict access to a data member, you can modify its visibility using the
protected metadata directive. The presence of this directive causes the Slice compiler to generate the data member with protected visibility. As a result, the member can be accessed only by the class itself or by one of its subclasses. For example, the
TimeOfDay class shown below has the
protected metadata directive applied to each of its data members:
The Slice compiler produces the following generated code for this definition:
For a class in which all of the data members are protected, the metadata directive can be applied to the class itself rather than to each member individually. For example, we can rewrite the
TimeOfDay class as follows:
Class Constructors in PHP
Classes have a constructor that assigns to each data member a default value appropriate for its type:
|Data Member Type||Default Value|
|First enumerator in enumeration|
You can also declare different default values for data members of primitive and enumerated types.
For derived classes, the constructor has one parameter for each of the base class's data members, plus one parameter for each of the derived class's data members, in base-to-derived order.
Pass the marker value
\Ice\None as the value of any optional data members that you wish to be unset.
Class Operations in PHP
Operations on classes are deprecated as of Ice 3.7. Skip this section unless you need to communicate with old applications that rely on this feature.
With the PHP mapping, operations in classes are not mapped at all into the corresponding PHP class. The generated PHP class is the same whether the Slice class has operations or not.
Value Factories in PHP
While value factories were necessary in previous versions of Ice when using classes with operations (a now deprecated feature) with the PHP mapping, value factories may be used for any kind of class and are not deprecated.
Value factories allow you to create classes derived from the PHP class generated by the Slice compiler, and tell the Ice run time to create instances of these classes when unmarshaling. For example, with the following simple interface:
You then create and register a value factory for your custom class with your Ice communicator: