Disable implicit conversion

[Eugene]

Hi!

What I want to do is pretty simple.  I need to subtract a ubyte from a
ubyte and store the result in a ubyte.  The problem is that DMD
implicitly wants to convert the ubytes into an integer, so it fails
when attempting to store the result into a ubyte.  (Int cannot be
converted to ubyte?)
The error message I get:

src\test.d(26): Error: cannot implicitly convert expression
(cast(int)u2 - cast(int)u1) of type int to ubyte