How to easily initialize a list of Tuples?

C# 6 adds a new feature just for this: extension Add methods. This has always been possible for VB.net but is now available in C#.

Now you don't have to add Add() methods to your classes directly, you can implement them as extension methods. When extending any enumerable type with an Add() method, you'll be able to use it in collection initializer expressions. So you don't have to derive from lists explicitly anymore (as mentioned in another answer), you can simply extend it.

public static class TupleListExtensions
{
    public static void Add<T1, T2>(this IList<Tuple<T1, T2>> list,
            T1 item1, T2 item2)
    {
        list.Add(Tuple.Create(item1, item2));
    }

    public static void Add<T1, T2, T3>(this IList<Tuple<T1, T2, T3>> list,
            T1 item1, T2 item2, T3 item3)
    {
        list.Add(Tuple.Create(item1, item2, item3));
    }

    // and so on...
}

This will allow you to do this on any class that implements IList<>:

var numbers = new List<Tuple<int, string>>
{
    { 1, "one" },
    { 2, "two" },
    { 3, "three" },
    { 4, "four" },
    { 5, "five" },
};
var points = new ObservableCollection<Tuple<double, double, double>>
{
    { 0, 0, 0 },
    { 1, 2, 3 },
    { -4, -2, 42 },
};

Of course you're not restricted to extending collections of tuples, it can be for collections of any specific type you want the special syntax for.

public static class BigIntegerListExtensions
{
    public static void Add(this IList<BigInteger> list,
        params byte[] value)
    {
        list.Add(new BigInteger(value));
    }

    public static void Add(this IList<BigInteger> list,
        string value)
    {
        list.Add(BigInteger.Parse(value));
    }
}

var bigNumbers = new List<BigInteger>
{
    new BigInteger(1), // constructor BigInteger(int)
    2222222222L,       // implicit operator BigInteger(long)
    3333333333UL,      // implicit operator BigInteger(ulong)
    { 4, 4, 4, 4, 4, 4, 4, 4 },               // extension Add(byte[])
    "55555555555555555555555555555555555555", // extension Add(string)
};

---

C# 7 will be adding in support for tuples built into the language, though they will be of a different type (System.ValueTuple instead). So to it would be good to add overloads for value tuples so you have the option to use them as well. Unfortunately, there are no implicit conversions defined between the two.

public static class ValueTupleListExtensions
{
    public static void Add<T1, T2>(this IList<Tuple<T1, T2>> list,
        ValueTuple<T1, T2> item) => list.Add(item.ToTuple());
}

This way the list initialization will look even nicer.

var points = new List<Tuple<int, int, int>>
{
    (0, 0, 0),
    (1, 2, 3),
    (-1, 12, -73),
};

But instead of going through all this trouble, it might just be better to switch to using ValueTuple exclusively.

var points = new List<(int, int, int)>
{
    (0, 0, 0),
    (1, 2, 3),
    (-1, 12, -73),
};

Yes! This is possible.

The { } syntax of the collection initializer works on any IEnumerable type which has an Add method with the correct amount of arguments. Without bothering how that works under the covers, that means you can simply extend from List<T>, add a custom Add method to initialize your T, and you are done!

public class TupleList<T1, T2> : List<Tuple<T1, T2>>
{
    public void Add( T1 item, T2 item2 )
    {
        Add( new Tuple<T1, T2>( item, item2 ) );
    }
}

This allows you to do the following:

var groceryList = new TupleList<int, string>
{
    { 1, "kiwi" },
    { 5, "apples" },
    { 3, "potatoes" },
    { 1, "tomato" }
};

c# 7.0 lets you do this:

  var tupleList = new List<(int, string)>
  {
      (1, "cow"),
      (5, "chickens"),
      (1, "airplane")
  };

If you don't need a List, but just an array, you can do:

  var tupleList = new(int, string)[]
  {
      (1, "cow"),
      (5, "chickens"),
      (1, "airplane")
  };

And if you don't like "Item1" and "Item2", you can do:

  var tupleList = new List<(int Index, string Name)>
  {
      (1, "cow"),
      (5, "chickens"),
      (1, "airplane")
  };

or for an array:

  var tupleList = new (int Index, string Name)[]
  {
      (1, "cow"),
      (5, "chickens"),
      (1, "airplane")
  };

which lets you do: tupleList[0].Index and tupleList[0].Name

Framework 4.6.2 and below

You must install System.ValueTuple from the Nuget Package Manager.

Framework 4.7 and above

It is built into the framework. Do not install System.ValueTuple. In fact, remove it and delete it from the bin directory.

note: In real life, I wouldn't be able to choose between cow, chickens or airplane. I would be really torn.