What the heck am i doing wrong? I'm just trying to create a 8 bit unsigned variable.

[H. S. Teoh]

On Fri, May 16, 2025 at 07:04:24PM +0000, WhatMeWorry via Digitalmars-d-learn wrote:
[...]
> void main()
> {
>     ubyte a;
>     a = a + 5; // onlineapp.d(11): Error: cannot implicitly convert expression `cast(int)a + 5` of type `int` to `ubyte`
[...]

Welcome to your first encounter with why I hate D's narrow integer
promotion rules.

Basically, `a + 5` gets promoted to int, and that's why it can't be
assigned back to `a`.  (Don't ask me why, that's just the way it is and
Walter has refused and probably will continue to refuse to change it.)

Ironically, this is OK:

```
	ubyte a;
	a += 5;
```

But writing it as `a = a + 5;` is not.

You can't just decide to use the `<op>=` form to work around this every
time either.  For example, how do you negate a ubyte?  Obviously, you
can't do this:

```
	ubyte a;
	a -=;
```

But writing it as `a = -a;` runs into the same error, for the same
reason.

Instead, you have to work around it with this baroque periphrasis:

```
	ubyte a;
	a = cast(ubyte) -a;
```

Does it make sense?

Yes, it's just a consequence of integer promotion rules.

Does it make sense?

Intuitively, absolutely not.

What's the solution?  Maybe this might interest you:

	https://forum.dlang.org/post/mailman.282.1631547531.21945.digitalmars-d@puremagic.com


T

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