Class VirtualMethod

A utility for keeping backwards compatibility on previously abstract methods (or similar replacements).

Before the replacement method can be made abstract, the old method must kept deprecated. If somebody still overrides the deprecated method in a non-sealed class, you must keep track, of this and maybe delegate to the old method in the subclass. The cost of reflection is minimized by the following usage of this class:

Define static readonly fields in the base class (BaseClass), where the old and new method are declared:

internal static readonly VirtualMethod newMethod =
    new VirtualMethod(typeof(BaseClass), "newName", parameters...);
internal static readonly VirtualMethod oldMethod =
    new VirtualMethod(typeof(BaseClass), "oldName", parameters...);

this enforces the singleton status of these objects, as the maintenance of the cache would be too costly else. If you try to create a second instance of for the same method/baseClass combination, an exception is thrown.

To detect if e.g. the old method was overridden by a more far subclass on the inheritance path to the current instance's class, use a non-static field:

 bool isDeprecatedMethodOverridden =
     oldMethod.GetImplementationDistance(this.GetType()) > newMethod.GetImplementationDistance(this.GetType());

// alternatively (more readable):
bool isDeprecatedMethodOverridden =
    VirtualMethod.CompareImplementationDistance(this.GetType(), oldMethod, newMethod) > 0

GetImplementationDistance(Type) returns the distance of the subclass that overrides this method. The one with the larger distance should be used preferable. this way also more complicated method rename scenarios can be handled (think of 2.9 TokenStream deprecations).

This is a Lucene.NET INTERNAL API, use at your own risk
Inheritance
System.Object
VirtualMethod
Namespace: Lucene.Net.Util
Assembly: Lucene.Net.dll
Syntax
public sealed class VirtualMethod : object

Constructors

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VirtualMethod(Type, String, Type[])

Creates a new instance for the given baseClass and method declaration.

Declaration
public VirtualMethod(Type baseClass, string method, params Type[] parameters)
Parameters
Type Name Description
Type baseClass
System.String method
Type[] parameters

Methods

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CompareImplementationDistance(Type, VirtualMethod, VirtualMethod)

Utility method that compares the implementation/override distance of two methods.

Declaration
public static int CompareImplementationDistance(Type clazz, VirtualMethod m1, VirtualMethod m2)
Parameters
Type Name Description
Type clazz
VirtualMethod m1
VirtualMethod m2
Returns
Type Description
System.Int32
  • > 1, iff m1 is overridden/implemented in a subclass of the class overriding/declaring m2
  • < 1, iff m2 is overridden in a subclass of the class overriding/declaring m1
  • 0, iff both methods are overridden in the same class (or are not overridden at all)
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GetImplementationDistance(Type)

Returns the distance from the baseClass in which this method is overridden/implemented in the inheritance path between baseClass and the given subclass subclazz.

Declaration
public int GetImplementationDistance(Type subclazz)
Parameters
Type Name Description
Type subclazz
Returns
Type Description
System.Int32

0 if and only if not overridden, else the distance to the base class.

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IsOverriddenAsOf(Type)

Returns, if this method is overridden/implemented in the inheritance path between baseClass and the given subclass subclazz.

You can use this method to detect if a method that should normally be final was overridden by the given instance's class.

Declaration
public bool IsOverriddenAsOf(Type subclazz)
Parameters
Type Name Description
Type subclazz
Returns
Type Description
System.Boolean

false if and only if not overridden.