Lots of bool operations shouldn't compile

[Oskar Linde]

Don Clugston skrev:
> Oskar Linde wrote:
>> Don Clugston skrev:
>>> Four examples, although it's only one bug. Almost all operations on 
>>> bool should be disabled, but I found the ones below a little amusing. 
>>> None of them should compile, but they all evaluate as "true".
>>>
>>> void main()
>>> {
>>>     if (true >= ireal.nan) { writefln("This is kind of ridiculous"); }
>>>     if (false >= ireal.nan) { writefln("This is kind of ridiculous"); }
>>>     if (true <> -2i) { writefln("NCEG operators too ??!!"); }
>>>     if (false != -2i) { writefln("and again"); }
>>> }
>>
>> According to the specification, booleans are a numeric type. true == 1 
>> and false == 0. So this error is not specific to bool.
>>
>> Try s/true/1/g and s/false/0/g and you will get the same results.
>>
>> The first two comparisons should be false I guess since they are 
>> unordered. The other two are correct.
> 
> OK, there's another bug in there, comparing an int with an imaginary 
> real should also not be legal.
> 
>     if (1 > -2i) { assert(0); }
>     if (1 > ireal.nan) { assert(0); }
> 
> Reals and ireals cannot be compared. Ever.

You are right. I didn't notice.

> 
>> (If it is wise to have bool as a numeric type is a different question.)
> 
> I think it's very hard to justify numeric operations on bools.
> (which is an _entirely_ different issue to implicit "!is null" in 
> conditionals, I wholeheartedly support if (p), while(1){} and assert(0) ).
> But I note that
> bool b = 7;
> is currently disallowed, while
> b+=5;
> compiles.
> There's no reason to write b++, it's just letting bugs in. Write b=true 
> instead. I hope that all such bug-breeding nonsense disappears. With a 
> one bit integer, it wasn't clear how such things should behave (every 
> other integral types wraps around, so b=5 should mean b=0 -- yuck!), but 
> hopefully it can be cleared up now.

I fully agree.

(But note that the current D bool is (sans bugs) semantically identical 
(as far as I can tell) to C99 and C++ bool, who both allows b+=5, et.al.)

/Oskar