Why code failed to compile for foo2?

[apz28]

On Sunday, 12 December 2021 at 00:02:25 UTC, Stanislav Blinov 
wrote:
> @apz28, I can't figure out the intent here. To convert result 
> of abs to an unsigned?

The function logic works only for unsigned type and the parameter 
value can be altered in body hence Unqual. If not Unqual, must 
declare a local var and make a copy. Just asking if this can be 
done to avoid a cast by caller