The following section from the Language Reference does not correspond to the current dmd compiler (v2.052, Windows) behaviour:
" Integer values cannot be implicitly converted to another type that cannot represent the integer bit pattern after integral promotion. For example: ubyte u1 = cast(byte)-1; // error, -1 cannot be represented in a ubyte ushort u2 = cast(short)-1; // error, -1 cannot be represented in a ushort uint u3 = cast(int)-1; // ok, -1 can be represented in a uint ulong u4 = cast(ulong)-1; // ok, -1 can be represented in a ulong " Both byte and short casts work all right.
