On Friday, 18 January 2019 at 17:09:52 UTC, Mek101 wrote:
Meaning that the byte type doesn't have a + operator.
Well, it DOES have a + operator, it just returns int that can be squished to a size if and only if the compiler proves it fits.
A bit of background: the C language was designed on a machine that did arithmetic in a fixed size register. It defined `int` to be at least the size of this register and for all arithmetic to be expanded to at least that same size.
In other words, anything smaller than an `int` is converted to an `int` before operations are done to it.
D (and C# via the CLR being designed in the same way, among other languages) inherited this rule from C. So a + a will be converted to int for anything smaller than int, like byte or short.
Now the difference between C and D is that C would let you assign that result right back to the small type without complaining, whereas D issues the error. Why?
The reason is the carry bit. Consider the case of 127 + 127. The answer is too big to fit in a signed byte; one bit will carry over and be dropped. D considers this potential data loss and wants you to make a conscious choice about it via an explicit cast.
If the compiler knows for certain the numbers will fit, it allows it. Like 64 + 5 will implicitly cast to a byte because the compiler sees the size of the result. But for runtime values, it is usually unsure and forces you to do the cast.
temp[fowardI] = cast(byte) (temp[fowardI] + temp[backwardI]); that will work.
