Question

I have managed to create my own IList sub class using some code i found on another thread on the MSDN. I have added some of my own methods and have tested the class in basic scenarios and it seems to be working fine.

The problem is that when i try and use the regular .ToList() method i am returned a List instead of my custom pList. Obviously i need to cast it to my new type but i am unsure how. Do i need to implement another method in my custom iList to allow it to be assigned with a different format?

My class is declared as shown below.

public class pList<T> : IList<T>

James

Answer 1

You won’t be able to cast a List<T> directly to pList<T>. You could make an extension method (just like ToList). Assuming your class has a constructor that takes an IEnumerable<T> to populate the list:

static class EnumerableExtensions
{
    static pList<T> ToPList<T>(this IEnumerable<T> sequence) { return new pList<T>(sequence); }
}

If your class doesn’t have such a constructor, you can either add one, or do something like this:

static class EnumerableExtensions
{
    static pList<T> ToPList<T>(this IEnumerable<T> sequence)
    {
        var result = new pList<T>();
        foreach (var item in sequence)
            result.Add(item);
        return result;
    }
}

my pList class does have a constructor that takes IEnumerable have added your extension method but i am still unable to see ToPList() within the List Am i missing something?

First, if you have such a constructor, and you want to convert an existing List<T> to a pList<T>, you can of course do this:

List<T> originalList = GetTheListSomehow();
var newList = new pList<T>(originalList);

To use an extension method, you have to make sure that the method is in scope. I didn’t add access modifiers to my example. Put internal or public in, as appropriate:

public static class EnumerableExtensions
{
    internal static pList<T> ToPList<T> //...

Also, if you want to use the extension method in a different namespace, you’ll have to have a using directive in scope. For example:

namespace A { public static class EnumerableExtensions { ...

Elsewhere:

using A;
// here you can use the extension method

namespace B
{
    public class C
    {
        ...

or

namespace B
{
    using A;
    // here you can use the extension method

    public class C
    {
        ...