Using C# IComparer in Unity game engine

Question

I am writing an Edge class for my graph for an A* implementation. I would want to later create a list of Edges and sort them based on edge weights using the IComparer interface.

Below is my implementation of Edge class inside Unity 4.5f

using UnityEngine;
using System.Collections;

public class Edge : IComparer {

    Node destination;
    int weight;

    public Edge(Node destinationNode, int cost)
    {
        destination = destinationNode;
        weight = cost;
    }

    public Node getDestination()
    {
        return destination;
    }

    public int getCost()
    {
        return weight;
    }

    int IComparer.Compare(System.Object a, System.Object b)
    {
        if (((Edge)a).getCost() == ((Edge)b).getCost()) return 0;
        else if (((Edge)a).getCost() > ((Edge)b).getCost()) return 1;
        else return -1;
    }
}

But Unity throws the below error

ArgumentException: does not implement right interface System.Collections.Generic.Comparer`1+DefaultComparer[Edge].Compare (.Edge x, .Edge y) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System.Collections.Generic/Comparer.cs:86)

I also tried using IComparer<Edge> but it throws error

The non generic type 'System.Collections.IComparer' cannot be used with type arguments

Unity also does not allow me to use IComparable as it does not understand when I try to use it :( it throws

" type or namespace not found "

I don't know whats wrong. Could someone please help me out?

Answer 1

I think Unity expects you to implement IComparable<Edge> (generic version of IComparable, please see http://msdn.microsoft.com/fr-fr/library/4d7sx9hd%28v=vs.110%29.aspx )

This implementation will be really close to yours, except it doesn't need casts (since input types are already some Edge)