Creating new properties in a struct, outside of said struct

Question

This is kind of hard to explain, so bear with me.

In PHP, if you wanted create a new property in a class, you could without doing anything. The following code would work perfectly.

    class testClass
{
    public function __construct()
    {
    }
}

$test = new testClass;
$test->propone = "abc";
echo $test->propone;

I would like to do the same thing, only in C# and with a struct. Is this possible?

Yes, I know, this sounds really clunky. I am trying to simulate a sort of associative array, where there is none. In my environment (NET Microframeworks), hashtables and dictionaries are not supported (yet).

Thanks!

Answer 1

As far as I know there's no way to add properties dynamically at runtime. Nor is there a way to add properties at compile-time aside from adding them directly to the declaration. In my opinion, this is good as it maintains the type-safety expected from C#.

However, couldn't you make a primitive hashtable using List<KeyValuePair<int, List<KeyValuePair<string, object>>>> and String.GetHashCode()? Something like the following (untested and part-pseudocode, but you get the idea):

class HashTable<T>
{
    private List<KeyValuePair<int, List<KeyValuePair<string, T>>>> _table = 
        new List<KeyValuePair<int, List<KeyValuePair<string, T>>>>();

    private void Set(string key, T value)
    {
        var hashcode = key.GetHashCode();
        List<KeyValuePair<string, T>> l;
        if(!_table.TryGetValue(hashcode, out l))
        {
            l = new List<KeyValuePair<string, T>>();
            _table.Add(hashcode, l);
        }

        T o;
        if(l.TryGetValue(key, out o))
        {
            if (o != value)
                l.Single(x => x.Key == key).Value = o;
        }
        else
            l.Add(new KeyValuePair(key, value));
    }

    private T Get(string key)
    {
        List<KeyValuePair<string, T>> l;
        object o;
        if(!(_table.TryGetValue(hashcode, out l) && 
            !l.TryGetValue(key, out o)))
        {
            throw new ArgumentOutOfRangeException("key");
        }

        return o;
    }
}

The following should help you with TryGetValue:

public bool TryGetValue<TKey, TValue>(this List<KeyValuePair<TKey, TValue>> list, 
    TKey key, out TValue value)
{
    var query = list.Where(x => x.Key == key);        
    value = query.SingleOrDefault().Value;
    return query.Any();
}

Answer 2

Don't simulate an associative array - go write one and use it.

Answer 3

In C# version 4.0, as released with .NET 4.0 and Visual Studio 2010, the new pseudo type dynamic can allow you to do what you want - though if you're new to C# (as you seem to be) it's likely the techniques involved will be a bit deep.

All you need to do is to implement the appropriate interface; once this is done, any client code that uses your object dynamically may access on-the-fly properties (and methods) much like your PHP example.

References if you want to know more ...

• Using Type dynamic (C# Programming Guide)
• What's the difference between dynamic(C# 4) and var?
• Fun With Method Missing and C# 4
• Dynamic in C# 4.0: Introducing the ExpandoObject