Specify the initial size forToList or ToArray

[linkdotnet]

Rationale

For performance-related reasons, folks can specify the initial size of a List<T> when creating one via the ctor:

var foo = new List<int>(1_000);

To specify the initial size of the underlying array to avoid resizing, which makes it a nice low-hanging fruit in performance-related scenarios where the rough size is known upfront.

Unfortunately, this doesn't work well with LINQ. There is no way of specifying the initial size like: foo.Where(...).ToList(size: 1_000);. Now, one can make the argument using for(each) loop and creating the list upfront would be the more sensible choice here. Sure, but that only helps so far.

When using Entity Framework often times I know exactly how many elements I get (or at most how many items). If the dataset returned is not only 100 elements, EF will (maybe?) have to resort to a lot of resizing internally if ToList(Async) is used.

While there are some workarounds (like AsAsyncEnumerable): They are not always the right tool and are error-prone.

Therefore: Is there any compelling reason against extending the API to allow an initial size?

[svick]

This has been previously discussed and rejected, see e.g. #83807 and #29620.

[linkdotnet]

Thanks for the link - yeah that is a dup then. I swear I tried to look for that in the current discussion, but it did not cross my mind to check the issues.