CODEWITHSUNDEEP
c#generics
user1205746
user1205746

Reputation: 3364

Generic class comparison

I would like to create a generic class Node as follow:

public class Node<T>
{
  public Node<T> Next;
  public Node<T> Previous;
  T Content;

  public Node<T>()
  {
  }
}

In my main (or from other class) I would like to compare items.. something like the following: (I use pseudo code to illustrate my idea, the code may or may not really work). Basically I would like to find if the item I have is in the list.

main()
{
  List<Node<T>> n = new List<Node<T>>()
  bool found = false;
  T v = new T();
  foreach (Node<T> i in n)
  {
    if i.Content== v
    {
       found = true;
    }
  }
}

I understand in order to compare 2 instances of a class, I have to derive my class from IEquitable, but I would like to know if T belongs to predefined classes that we have been using all the times like int, double, string ... I do not want to redefine those classes but would expect the comparison to work and use the default comparator. How do I write the above so that c# would accept it and throw out a syntax error?

    if i.Content== v
    {
       found = true;
    }

I have tried 

if (T)i.Content == (T)v 
{
  ...
}

The compiler does not seem to like it. Actually, I did the following:

 Node<T> r = n.Where(x=> (T)x.Content==(T)v).FirstOrDefault()

The error I got was: Operator == could not applied to operands of type 'T' and 'T' Please advise. Thanks!

Upvotes: 1

Views: 67

Answers (3)

Abion47
Abion47

Reputation: 24661

You could change your Node<T> declaration to the following:

public class Node<T> where T : IEquatable<T>

Then you would be able to use:

if (i.Content.Equals(v))
    // ...

Upvotes: 1

Lee
Lee

Reputation: 144126

You can use IEqualityComparer<T>:

var comp = EqualityComparer<T>.Default;
if (comp.Equals(i.Content, v)) {
   ...
}

Upvotes: 4

Luaan
Luaan

Reputation: 63722

There is no way to specify operators in generic constraints (with the exception of the parameter-less constructor, if you consider it an operator).

If you need some way of comparison, you need to use a method. Either use Equals, or add some interface like IComparable<T> as a generic constraint.

Upvotes: 0

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