Initialize list with both a single object and another list of objects

Question

I want to initialize a list with an object and a list of objects in that specific order. Currently, I am doing:

List<MyObject> list = new List<MyObject>();
list.Add(object1); // object1 is type MyObject
list.AddRange(listOfObjects); // listOfObjects is type List<MyObject>

I was hoping to consolidate that into an initialization statement (the syntax is wrong of course):

List<MyObject> newList = new List<MyObject>() { object1, listOfObjects };

Is there a way to do this concisely?

Answer 1

If the order of the elements is not important, you can use:

List<MyObject> newList = new List<MyObject>(listOfObjects) { object1 };

This works by using the List<T> constructor which accepts an IEnumerable<T>, then the collection initializer to add the other items. For example, the following:

static void Main()
{
    int test = 2;
    List<int> test2 = new List<int>() { 3, 4, 5 };
    List<int> test3 = new List<int>(test2) { test };

    foreach (var t in test3) Console.WriteLine(t);

    Console.ReadKey();
}

Will print:

3
4
5
2

Note that the order is different than your original, however, as the individual item is added last.

If the order is important, however, I would personally just build the list, placing in your first object in the initializer, and calling AddRange:

List<MyObject> newList = new List<MyObject> { object1 };
newList.AddRange(listOfObjects);

This makes the intention very clear, and avoids construction of temporary items (which would be required using LINQ's Concat, etc).