byte + byte = int: why?

[Paul Backus]

On Sunday, 29 August 2021 at 15:42:18 UTC, Ali Çehreli wrote:
> Depending on the situation, you may want to use std.conv.to, 
> which does a value range check and throws an exception to 
> prevent an error:
>
>     byte foo(byte a, byte b) {
>       import std.conv : to;
>       return (a + b).to!byte;
>     }
>
>     void main() {
>       foo(42, 42);    // Works
>       foo(100, 100);  // Throws ConvOverflowException
>     }

I was going to suggest `std.experimental.checkedint` as an 
alternative here, but it turns out that it does integer promotion 
too--`Checked!byte + Checked!byte == Checked!int`.

This seems obviously wrong to me, but according to run.dlang.io 
it's always worked that way.