Treating the abusive unsigned syndrome

[Andrei Alexandrescu]

Don wrote:
> Andrei Alexandrescu wrote:
>> One fear of mine is the reaction of throwing of hands in the air "how 
>> many integral types are enough???". However, if we're to judge by the 
>> addition of long long and a slew of typedefs to C99 and C++0x, the 
>> answer is "plenty". I'd be interested in gaging how people feel about 
>> adding two (bits64, bits32) or even four (bits64, bits32, bits16, and 
>> bits8) types as basic types. They'd be bitbags with undecided sign 
>> ready to be converted to their counterparts of decided sign.
> 
> Here I think we have a fundamental disagreement: what is an 'unsigned 
> int'? There are two disparate ideas:
> 
> (A) You think that it is an approximation to a natural number, ie, a 
> 'positive int'.
> (B) I think that it is a 'number with NO sign'; that is, the sign 
> depends on context. It may, for example, be part of a larger number. 
> Thus, I largely agree with the C behaviour -- once you have an unsigned 
> in a calculation, it's up to the programmer to provide an interpretation.
> 
> Unfortunately, the two concepts are mashed together in C-family 
> languages. (B) is the concept supported by the language typing rules, 
> but usage of (A) is widespread in practice.

In fact we are in agreement. C tries to make it usable as both, and 
partially succeeds by having very lax conversions in all directions. 
This leads to the occasional puzzling behaviors. I do *want* uint to be 
an approximation of a natural number, while acknowledging that today it 
isn't much of that.

> If we were going to introduce a slew of new types, I'd want them to be 
> for 'positive int'/'natural int', 'positive byte', etc.
> 
> Natural int can always be implicitly converted to either int or uint, 
> with perfect safety. No other conversions are possible without a cast.
> Non-negative literals and manifest constants are naturals.
> 
> The rules are:
> 1. Anything involving unsigned is unsigned, (same as C).
> 2. Else if it contains an integer, it is an integer.
> 3. (Now we know all quantities are natural):
> If it contains a subtraction, it is an integer [Probably allow 
> subtraction of compile-time quantities to remain natural, if the values 
> stay in range; flag an error if an overflow occurs].
> 4. Else it is a natural.
> 
> 
> The reason I think literals and manifest constants are so important is 
> that they are a significant fraction of the natural numbers in a program.
> 
> [Just before posting I've discovered that other people have posted some 
> similar ideas].

That sounds encouraging. One problem is that your approach leaves the 
unsigned mess as it is, so although natural types are a nice addition, 
they don't bring a complete solution to the table.


Andrei