In D, it appears that dynamic arrays (at least by default) use a
ulong as their key type. They are declared like this:
```
string[] dynamicArray;
```
I imagine that using a 64-bit value as the key would be slower
than using 32 bits or 16 bits, and 64 bits is way overkill for
nearly everything. However, if I declare the array as
`string[uint] myArray;` or `string[ushort] myArray`, it's treated
as an associative array. This means that I don't get to do the
things I want to do with a dynamic array, such as appending.
So I have some questions:
Is there a way to declare a dynamic array with a uint, ushort, or
ubyte key?
If there was, would it really be faster?
Is an associative array with a ushort key faster than a dynamic
array with a ulong key?
