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.NET Double Reference

, 31 Mar 2011 CPOL
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Simple class to encapsulate a double reference


The DoubleReference class below wraps a reference which gives one reference to references. When used, they act like double pointers in C and in some cases can increase efficiency a great deal.


Double pointers in C give one the ability to have objects point to a "placeholder". The placeholder can change value and all the objects pointing to the placeholder will see the change. The placeholder itself is usually a reference/pointer to the object of interest. This can be achieved similarly in .NET by wrapping a reference in a class.

Using the Code

Use the class...

public class DoubleReference<T>
    public T Reference { get; set; }
    public DoubleReference(T reference) { Reference = reference; }
    public static implicit operator T(DoubleReference<T> x) { return x.Reference; }
    public static T operator ~(DoubleReference<T> x) { return x.Reference; }
} you would any reference but simply wrap them with this class. You can provide a direct link to a reference but wrap it in a property of the original type. This allows complete transparency.

DoubleReference<Test2> reff;
public Test2 RootTest { get { return reff.Reference; } set { reff.Reference = value; } }

Here we have a double reference placeholder. RootTest simply wraps the double reference and returns whatever it points to. Alternatively, we could expose the double reference if we want to avoid possible issues that changes to RootTest might incur. We could also remove the setter for Root Test.

The idea here is that we can create a single DoubleReference class and pass that around. As long as objects that reference this object do not change their reference, any changes to the double reference's reference will "propagate" to all objects using it.

You can use this, for example, in a collection where every element in the collection has a "Current" property. The Current property points to some current element. When the value has to change, it should propagate to all elements. By using a double reference, you can do this instantaneously at the cost of the extra memory.


  • 29th March, 2011: Initial version


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


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Comments and Discussions

QuestionWhy the operator ~? PinmemberDon Kackman31-Mar-11 11:44 
AnswerRe: Why the operator ~? PinmemberJon_Slaughter31-Mar-11 14:54 
Initially I made the reference private and I needed a way to dereference it. ~ sort of acts like -> in C++.
The code is mainly a demonstration of how to emulate a double pointer in C. I wrote it up for my own code so I could have a bunch of objects reference one object and I could change just a single reference rather than having to go through all the objects.
....----+ -> Double Reference -> object ref
instead of
Obj1 -> object ref
.... -> object ref
Objn -> object ref

By simply changing the reference pointed to by the double reference all the objects 1 - n will be "updated" instantaneously.
I didn't initially want to give the objects the ability to change their reference(for safety reasons) but still needed a way to access the reference. Using a property or a unary operator achieves the same result. Unfortunately the unary operator must be wrapped in parenthesis before accessing the reference members. This makes it less useful but generally is still shorter to type.
In any case if you are ok with changing the reference to a public field then you don't need it.
GeneralRe: Why the operator ~? PinmemberDon Kackman1-Apr-11 8:02 
GeneralRe: Why the operator ~? [modified] PinmemberJon_Slaughter1-Apr-11 9:39 
GeneralRe: Why the operator ~? PinmemberDon Kackman1-Apr-11 12:00 
GeneralRe: Why the operator ~? PinmemberJon_Slaughter1-Apr-11 15:09 
GeneralSingle-item arrays... Pinmembersupercat931-Mar-11 6:35 
GeneralRe: Single-item arrays... PinmemberJon_Slaughter31-Mar-11 10:20 

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