Create Dictionary-style collection initializer on custom class [duplicate]

Answer 1

Why not use a class that inherits from Dictionary?

public class PairDictionary : Dictionary<int, string>
{
}

private static void Main(string[] args)
{
    var temp = new PairDictionary
    {
        {0, "bob"},
        {1, "phil"},
        {2, "nick"}
    };

    Console.ReadKey();
}

You could also create your own collection (I suspect it is the case because you have the same Value1 for two items, so T1 doesn't act as a key in your example) that do not inherit from Dictionary.

If you want to use the syntactic sugar of collection initializer, you would have to provide a Add method that takes 2 arguments (T1 and T2 which are int and string in your case).

public void Add(int value1, string value2)
{
}

See Custom Collection Initializers

Answer 2

The syntax you're looking for is not provided by the object that is being used with the dictionary, it is the dictionary collection itself. If you need to be able to use a collection initializer then you'll need to use an existing collection (like Dictionary) or implement a custom collection to house it.

Otherwise you're basically limited to:

var temp = new Pair<int, string>[]
    {
        new Pair(0, "bob"),
        new Pair(1, "phil"),
        new Pair(0, "nick")
    };

Answer 3

public class Paircollection<T1, T2> : List<Pair<T1, T2>>
{
    public void Add(T1 value1, T2 value2)
    {
        Add(new Pair<T1, T2>(value1, value2));
    }
}

and then

var temp = new Paircollection<int, string>
{
    {0, "bob"},
    {1, "phil"},
    {0, "nick"}
};

will work. Essentially you're just creating a version of List<Pair<T1,T2>> that knows how to do the right Add things.

This is obviously expandable to any other class than Pair (in a way that the dictionary solutions aren't).

Thanks to Yuriy Faktorovich for helping me with my initial understanding and the linked question for pointing me in teh right direction.

Answer 4

To get the custom initialization to work like Dictionary you need to support two things. Your type needs to implement IEnumerable and have an appropriate Add method. You are initializing an Array, which doesn't have an Add method. For example

class PairList<T1, T2> : IEnumerable
{
    private List<Pair<T1, T2>> _list = new List<Pair<T1, T2>>();

    public void Add(T1 arg1, T2 arg2)
    {
        _list.Add(new Pair<T1, T2>(arg1, arg2));
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return _list.GetEnumerator();
    }
}

and then you can do

var temp = new PairList<int, string>
{
    {0, "bob"},
    {1, "phil"},
    {0, "nick"}
};