Do Where and OfType preserve List capacity?

I did a quick test using LINQPad and it looks as though .Select() does not necessarily preserve capacity. For .Where() and .OfType() the capacity depends on the count, though it doesn't necessarily match it. In my case .Select() reduced the capacity to match the count. .Where() and .OfType() halved the capacity when it could contain the result, and preserved the capacity when it couldn't. This doesn't answer how it determines the exact capacity to use in any case.

List<object> fruits = new()
{
    "Mango",
    "Orange",
    null,
    "Apple",
    3.0,
    "Banana"
};

Console.WriteLine($"Original - Capactity: {fruits.Capacity}; Count: {fruits.Count()}");

List<object> everything = fruits.Select(x => x).ToList();
Console.WriteLine($"Selected - Capactity: {everything.Capacity}; Count: {everything.Count()}");

List<object> hasN = fruits.Where(x => x?.ToString()?.Contains("n") ?? false).ToList();
Console.WriteLine($"Whered   - Capactity: {hasN.Capacity}; Count: {hasN.Count()}");

List<string> isString = fruits.OfType<string>().ToList();
Console.WriteLine($"OfTyped  - Capactity: {isString.Capacity}; Count: {isString.Count()}");

List<object> notNull = fruits.Where(x => x != null).ToList();
Console.WriteLine($"Whered 2 - Capactity: {notNull.Capacity}; Count: {notNull.Count()}");

/* Output
Original - Capactity: 8; Count: 6
Selected - Capactity: 6; Count: 6
Whered   - Capactity: 4; Count: 3
OfTyped  - Capactity: 4; Count: 4
Whered 2 - Capactity: 8; Count: 5
*/

posted 5 days ago

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rcmosher‭

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