Yet another slap on the hand by implicit bool to int conversions

[Daniel Gibson]

Am 20.06.2011 15:31, schrieb Steven Schveighoffer:
> On Mon, 20 Jun 2011 09:17:56 -0400, Daniel Gibson
> <metalcaedes at gmail.com> wrote:
> 
>> Am 20.06.2011 14:47, schrieb Steven Schveighoffer:
>>> On Sun, 19 Jun 2011 19:42:22 -0400, bearophile
>>> <bearophileHUGS at lycos.com> wrote:
>>>
>>>> Timon Gehr:
>>>>
>>>>> Maybe DMD could warn on nonsense of the form x != x.
>>>>
>>>> Right. This thread is very good food for this enhancement request of
>>>> mine:
>>>> http://d.puremagic.com/issues/show_bug.cgi?id=5540
>>>>
>>>> Vote for this enhancement :-)
>>>
>>> I don't think this is a good idea.  Generic code could result in an
>>> error where there shouldn't be.  For example:
>>>
>>> int foo(T)()
>>> {
>>>    if(T.sizeof == char.sizeof)
>>>      ...
>>> }
>>>
>>> Would this fail to compile where T == char?  What about if T == ubyte?
>>>
>>> Generic programming sometimes results in silly code that is perfectly
>>> acceptable as generic code, and we need to take this into account before
>>> making decisions assuming a person is writing the code.
>>>
>>> -Steve
>>
>> It probably makes more sense to use static if in that case - and static
>> if could be an exception for these rules.
> 
> static if has different semantics than if (it doesn't create a scope),
> so maybe I want to use if.  But even so, static if is just as likely to
> contain these bugs as a normal if.  Both use an expression to determine
> whether the if should run or not, and there are quite a few constructs
> that can be used in a static if expression.
> 

Disallowing some things in if that are allowed in static if at least
catch most bugs of this kind because normal if is more common.

Maybe, as an alternative, "nonsensical" expressions could be allowed if
template parameters are involved. Don't know how hard it is to implement
this, though.

Another alternative: nonsensical expressions need to be enclosed by an
extra pair of parenthesis.
I think I have seen this for cases like if( (x=foo()) ) {}, meaning if(
foo() != 0), but x is assigned that value at the same time (so you could
as well write "if( (x=foo()) != 0)", but I don't remember in what
language (D doesn't allow it). Maybe it was a warning of g++?

Cheers,
- Daniel