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Indexers - make your classes act like arrays

adamkdean profile image Adam K Dean ・2 min read

Indexers are great, I've only really started using them consciously today, but they're a great discovery I'll be sure to incorporate into more of my code from now on.

As you can see here, we have a class, but we access a value as if it was an array, or a Hashtable. Just think of how you could use this!

VarClass vc = new VarClass();
vc["key"] = "value";
Console.WriteLine(vc["key"].ToString());

The code is really simple too, it's simply like a property with an input, here we just put a layer on top of a Hashtable, you can of course add something more useful, but this shows you how it works:

class VarClass
{
    private Hashtable ht = new Hashtable();

    public object this[object key]
    {
        get
        {
            return ht[key];
        }
        set
        {
            ht[key] = value;
        }
    }
}  

As you can see, you take the object they put within the square brackets as a parameter, and you make a property but as the name you put the keyword this, referring to the actual class object.

I just think it's so simply, yet so awesome..

I actually came across this whilst writing a simple Hashtable clone for someone over at Dream.In.Code. For the sake of your dying curiosity I will post the awesome class here:

class HashtableEx
{
    private List<object> keys = new List<object>();
    private List<object> values = new List<object>();

    public object this[object key]
    {
        get
        {
            int index = keys.IndexOf(key);
            if (index == -1) return null;
            else return values[index];
        }
        set
        {
            if (keys.Contains(key))
            {
                int index = keys.IndexOf(key);
                values[index] = value;
            }
            else
            {
                keys.Add(key);
                values.Add(value);
            }
        }
    }

    public object Get(object key)
    {
        int index = keys.IndexOf(key);
        return values[index];
    }

    public void Add(object key, object value)
    {
        keys.Add(key);
        values.Add(value);
    }

    public void Remove(object key)
    {
        int index = keys.IndexOf(key);
        keys.RemoveAt(index);
        values.RemoveAt(index);
    }

    public void Clear()
    {
        keys = new List<object>();
        values = new List<object>();
    }
}

Use it like so:

static void Main()
{
    HashtableEx ht = new HashtableEx();

    ht["hello"] = "world";

    Console.WriteLine("Value of \"hello\": {0}", ht["hello"]);
    Console.WriteLine("Type of \"hello\": {0}", ht["hello"].GetType());

    Console.ReadKey();
}

Which gives you the output:

Value of "hello": world
Type of "hello": System.String

Posted on by:

adamkdean profile

Adam K Dean

@adamkdean

Principal Network Engineer / Master of Engineering (Mechanical) student

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