unsigned policy

[Andrei Alexandrescu (See Website For Email)]

Henning Hasemann wrote:
> I know this is a more general questions as it applies to C and C++ as well,
> but somewhere I have to ask and actually D is what Im coding in:
> 
> Should one try to use uint in favor of int whenever one knows for sure the value
> wont be negative? That whould be a bit more expressive but on the other hand
> sometimes leads to type problems.
> For example, when having things like this:
> 
> T min(T)(T a, T b) {
>   return a < b ? a : b;
> }
> 
> Here you whould need to ensure to cast values so they share a common type.
> 
> How do you code? Do you use uint whenever it suitable reflects the data to
> store (eg a x-y-position on the screen) or only when necessary?

Current D botches quite a few of the arithmetic conversions. Basically 
all conversions that may lose value, meaning, or precision should not be 
allowed implicitly. Walter is willing to fix D in accordance to that 
rule, which would yield an implicit conversion graph as shown in:

http://erdani.org/d-implicit-conversions.pdf

Notice that there is no arrow e.g. between int and uint (loss of 
meaning), or between int and float (loss of precision). But there is an 
arrow from int and uint to double, because double is able to represent 
them faithfully.

If we are nice, we may convince Walter to implement that soon (maybe in 
1.006?) but it must be understood that the tighter rules will prompt 
changes in existing code.

To answer your question, with the new rules in hand, using unsigned 
types will considerably increase your expressiveness and your ability to 
detect bugs statically. Also, by the new rules ordering comparisons 
between mixed-sign types will be disallowed.


Andrei