Andrei Alexandrescu wrote:
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
Well, it does make unsigned numbers (case (B)) quite obscure and
low-level. They could be renamed with uglier names to make this clearer.
But since in this proposal there are no implicit conversions from uint
to anything, it's hard to do any damage with the unsigned type which
results.
Basically, with any use of unsigned, the compiler says "I don't know if
this thing even has a meaningful sign!".
Alternatively, we could add rule 0: mixing int and unsigned is illegal.
But it's OK to mix natural with int, or natural with unsigned.
I don't like this as much, since it would make most usage of unsigned
ugly; but maybe that's justified.
