Creating a new type, to get strong-ish type checking and restrict usage to certain operations, using struct perhaps

[Cecil Ward via Digitalmars-d-learn]

On Friday, 21 July 2017 at 18:49:21 UTC, Cecil Ward wrote:
> I was think about how to create a new type that holds packed 
> bcd values, of a choice of widths, that must fit into a 
> uint32_t or a uint64_t (not really long multi-byte objects). I 
> am not at all sure how to do it. I thought about using a 
> templated struct to simply wrap a uint of a chosen width, and 
> perhaps use alias this to make things nicer.

I guess part of my question, which I didn't really highlight well 
enough, is the issue of strong typing. Example: physical units 
types, such as amps and volts, implemented as say a double or 
float or real (want to template that) but disallow evil 
assignments, comparisons, addition etc of mixed types. Another 
one would be the prevention of mixing pounds and pence by 
straight addition, or straight comparisons and blocking straight 
assignment. I'm assuming in the latter case you might use a 
machine-architecture native integral type of whatever width, 
again templating wanted. These are all really old requests, I'm 
sure, but I would appreciate a start as to how to implement the 
strong type checking in D without too much pain.

Going back to the original example of packed bcd stored in a 
uint64_t say, first thing is that I want to ban illegal mixing of 
arbitrary binary values in ordinary uint64_tmtypes with decimal 
types, again no assignment, addition, comoarisons etc across 
types at all allowed. And no friendly automagically conversions 
from packed bcd to binary on the fly either - I want to treat 
that kind of usage as a straight bug by the user, for the moment 
at least, anyway, as I don't want to encourage silent horrible 
inefficiency creeping in.