How to return a null/default value when using generics that support objects/structs?

Question

I'm doing some dynamic A.I. programming and to avoid having to create so many different classes for each use case, so that the parameters can be passed correctly, I thought I'd use an an object bag/container, akin to a dictionary.

In order to support it fully generic, I made the key a Type parameter so I can use it in other projects, which works fine. My issue is, I want to support objects and structs so when it comes to implementing a TryGet style function, I don't know how to assign the out parameter.

Here is my class:

using System;
using System.Collections.Generic;

namespace mGuv.Collections
{
    public class ObjectBag<TKey>
    {
        private Dictionary<Type, Dictionary<TKey, object>> _objects = new Dictionary<Type, Dictionary<TKey, object>>();

        public ObjectBag()
        {
        }

        private bool HasTypeContainer<T>()
        {
            return _objects.ContainsKey(typeof(T));
        }

        public bool HasKey<T>(TKey key)
        {
            if (HasTypeContainer<T>())
            {
                return _objects[typeof(T)].ContainsKey(key);
            }

            return false;
        }

        public void Add<TIn>(TKey key, TIn value)
        {
            if(!HasTypeContainer<TIn>())
            {
                _objects.Add(typeof(TIn), new Dictionary<TKey, object>());
            }

            _objects[typeof(TIn)].Add(key, value);
        }

        public bool TryGet<TOut>(TKey key, out TOut value)
        {
            if (HasKey<TOut>(key))
            {
                value = (TOut)_objects[typeof(TOut)][key];
                return true;
            }

            // As expected, I can't assign value to null
            value = null; 

            // I also can't just return false as value hasn't been assigned
            return false;
        }
    }
}

Is there anyway to assign value to the default of anything that is passed in?

I.e. I want to be able to do:

ObjectBag<string> myBag = new ObjectBag();
myBag.Add<int>("testInt", 123);
myBag.Add<TestClass>("testClass", new TestClass();
myBag.TryGet<int>("testInt", out someInt);
myBad.TryGet<TestClass>("testClass", out someTestClass);

I don't want to use ref, as that requires initializing the variable before passing it in.

You can use [`default(T)`](https://msdn.microsoft.com/en-us/library/xwth0h0d.aspx). — Sebastian Schumann, Sep 17 '15 at 09:40
@Verarind, yeah you're correct, thanks. For some reason I thought `default` only worked on value types. — mGuv, Sep 17 '15 at 09:42

score 1 · Accepted Answer · answered Sep 17 '15 at 09:41

1

Nevermind, I thought default only worked for structs/value types.

I can just do:

value = default(TOut);

I should really research more before asking a question. I'll leave it up in case anyone else is silly like me.

answered Sep 17 '15 at 09:41

mGuv

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How to return a null/default value when using generics that support objects/structs?

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