capacity
fn
size_t capacity(T)(T[] arr) @property pure nothrow @trusted(Property) Gets the current _capacity of a slice. The _capacity is the size that the slice can grow to before the underlying array must be reallocated or extended.
If an append must reallocate a slice with no possibility of extension, then 0 is returned. This happens when the slice references a static array, or if another slice references elements past the end of the current slice.
Note
The _capacity of a slice may be impacted by operations on other slices.