Bools reloaded

[Ivan Senji]

Oskar Linde wrote:
> && and || controls the program flow. 

If's and while's containing them control program flow (or I didn't get 
something right?)

> They are not algebraic operators.

They are logic operators. (Ok algebraic if we are talking about Boolean 
algebra).

> &,|,~,^ are real operators that also maps directly onto machine
> instructions on most cpu architectures. 

Sure they are, and I use them all the time on ints.

> Their meaning would be well defined
> for bools. 

Not really:
bool a = //somehow 2
bool b = //somehow 4
a && b == true && true == true
a & b == 0x0010 & 0x0100 == 0x0000 == false,

I mean they would work but only if true == always 1 and false == always 0.

> && and || requires branching and are therefore much less
> efficient (even though this can be optimized away in many cases). 
> 
> Also, not allowing ^ for bools would mean that code that reads a^b today
> would have to be rewritten as:
> 
> (a && !b) || (!a && b).
> 

Oops, forgot about that one, so ^ can stay :)

> 
>>>Why should &,|,^,~ not be defined
>>>and allowed for bool? It would be problematic and inconsistent not
>>>having non-short-circuit operators for booleans.
>>
>>I learned from xs0's reply that Java uses &,| for non-short-circuit
>>evaluation when arguments are of type bool. As D doesn't have a bool in
>>the Java meaning I don't think making & anything but bitwise operator
>>makes sense.
> 
> 
> Huh? There have been regular discussions on the D newsgroups about bool
> since atleast 2001. 

Tell me about it, I think it is an neverending topic for D. Maybe even 
if Walter got bools 'right' some people would be complaining.

> Almost all threads about this have people arguing for
> the introduction of a logical (as opposed to the current numerical) bool
> type similar (not necessarily identical) to the Java boolean. Isn't this
> what we are discussing here too?

I think so.
In the paragraf you replyed to I was just trying to say that having &,| 
and ^ for bools only has meaning f they are strict logic bools and not 
numeric.

>>>>>(they mean very different things for integers). "&" normally means
>>>>>"bitwise and", but a pure bool doesn't have any bits.
>>>>>Is it legal to cast from a bool to some other type?
>>>>
>>>>
>>>>I'm not against casting but implicit conversions are bad.
>>>
>>>
>>>Do you mean that all implicit conversions are bad? Are the integer
>>>promotion rules bad?
>>
>>Ofcourse not. But with bools yes.
> 
> 
> I read your statement as meaning that all implicit conversions are bad. I
> was merely interested in why you thought so. :)

Well, I think I would be crazy to think that ;)