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).

Note

This API is for internal purposes only and might change in incompatible ways in the next release.

Inheritance

System.Object

VirtualMethod

Inherited Members

System.Object.Equals(System.Object)

System.Object.Equals(System.Object, System.Object)

System.Object.GetHashCode()

System.Object.GetType()

System.Object.MemberwiseClone()

System.Object.ReferenceEquals(System.Object, System.Object)

System.Object.ToString()

Namespace: Lucene.Net.Util

Assembly: Lucene.Net.dll

Syntax

public sealed class VirtualMethod

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
System.Type	baseClass
System.String	method
System.Type[]	parameters

Exceptions

Type	Condition
System.InvalidOperationException	if you create a second instance of the same `baseClass` and method declaration combination. This enforces the singleton status.
System.ArgumentException	If `baseClass` does not declare the given method.

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
System.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
System.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
System.Type	subclazz

Returns

Type	Description
System.Boolean	`false` if and only if not overridden.