Creating N objects and adding them to a list

Question

I have a method which takes in N, the number of objects I want to create, and I need to return a list of N objects.

Currently I can do this with a simple loop:

Answer 1

You can use the Range to create a sequence:

return Enumerable.Range(0, count).Select(x => new MyObj { bar = foo });

If you want to create a List, you'd have to ToList it.

Mind you though, it's (arguably) a non-obvious solution, so don't throw out the iterative way of creating the list just yet.

Answer 2

You can Use Enumerable.Repeat

IEnumerable<MyObject> listOfMyObjetcs = Enumerable.Repeat(CreateMyObject, numberOfObjects);

For more info read https://msdn.microsoft.com/en-us/library/bb348899(v=vs.110).aspx

Answer 3

You could create generic helper methods, like so:

// Func<int, T>: The int parameter will be the index of each element being created.

public static IEnumerable<T> CreateSequence<T>(Func<int, T> elementCreator, int count)
{
    if (elementCreator == null)
        throw new ArgumentNullException("elementCreator");

    for (int i = 0; i < count; ++i)
        yield return (elementCreator(i));
}

public static IEnumerable<T> CreateSequence<T>(Func<T> elementCreator, int count)
{
    if (elementCreator == null)
        throw new ArgumentNullException("elementCreator");

    for (int i = 0; i < count; ++i)
        yield return (elementCreator());
}

Then you could use them like this:

int count = 100;

var strList = CreateSequence(index => index.ToString(), count).ToList();

string foo = "foo";
var myList = CreateSequence(() => new MyObj{ Bar = foo }, count).ToList();