API proposal: List<T>.CapacityGrowthPercentage

[chucker]

Background and Motivation

List<T> has a Capacity property, which core sounds with its underlying array’s length. It defaults to 4, but can be manually set in a constructor overload or in the aforementioned property.

When adding items, EnsureCapacity will, if needed, grow the capacity so additional items fit. This is currently hardcoded to double the previous value. I.e., if you add a fifth item, the capacity becomes 8. Doubling was presumably chosen as an adequate compromise for typical use. Note, however, that capacity increases require copying the entire existing list to a new internal array.

Proposed API

public short CapacityGrowthPercentage { get; set; }

Usage examples

In most cases, you’ll use List<T> as before. The default CapacityGrowthPercentage is 100; the capacity grows by 100% each time.

For cases where you anticipate a list that

• is large to begin with,
• may grow, but not by huge amounts,
  you might set it to a much lower value:

var listWithManyItems = new List(new[] { 0, 1, 2, 3 })
{
    CapacityGrowthPercentage = 10
}

// grows the capacity from its default 4
// by 10%, rounded up, to 5
listWithManyItems.Add(4);

[davidfowl]

Where did you run into this being a problem in practice?

[lechu445]

similar issue #53128