What would happen if DMD would issue a compiler warning for untested return values?

bool somefunc() { ... }

void main() {
  somefunc();//warning: untested return value
  auto b = somefunc();//OK
}

Especially useful for C or OS functions returning error values or handles.

L.

PS. might even be worth a compiler error.

Lionello Lunesu wrote:
> What would happen if DMD would issue a compiler warning for untested return values?
> 
> bool somefunc() { ... }
> 
> void main() {
>   somefunc();//warning: untested return value
>   auto b = somefunc();//OK
> }
> 
> Especially useful for C or OS functions returning error values or handles.
> 
> L.
> 
> PS. might even be worth a compiler error.

I regularly use functions I don't need the return values of, so I wouldn't like this change.

On the other hand, Walter might stop using printf() all over Phobos... :P
Nah, not worth it. Besides, the fact that functions like printf() have a return value is probably enough reason for Walter not to make such a change.

Frits van Bommel wrote:
> Lionello Lunesu wrote:
>> What would happen if DMD would issue a compiler warning for untested return values?
>>
>> bool somefunc() { ... }
>>
>> void main() {
>>   somefunc();//warning: untested return value
>>   auto b = somefunc();//OK
>> }
>>
>> Especially useful for C or OS functions returning error values or handles.
>>
>> L.
>>
>> PS. might even be worth a compiler error.
> 
> I regularly use functions I don't need the return values of, so I wouldn't like this change.
> 
> On the other hand, Walter might stop using printf() all over Phobos... :P
> Nah, not worth it. Besides, the fact that functions like printf() have a return value is probably enough reason for Walter not to make such a change.

LOL, really?
What does printf return? (what about writef?)

Frits van Bommel wrote:
> Lionello Lunesu wrote:
>> What would happen if DMD would issue a compiler warning for untested return values?
> I regularly use functions I don't need the return values of, so I wouldn't like this change.
> 
> On the other hand, Walter might stop using printf() all over Phobos... :P
> Nah, not worth it. Besides, the fact that functions like printf() have a return value is probably enough reason for Walter not to make such a change.

I tried this back in the '80s. It's one of those things that sure sounds like a good idea. The problem is, there are just too many cases where the return value is legitimately ignored (like printf's), so you wind up filling your code with chaff like:

	cast(void) printf( ... );

After a few dozen of those, it starts looking like a bad idea <g>.

Hasan Aljudy wrote:
> Frits van Bommel wrote:
>> Lionello Lunesu wrote:
>>> What would happen if DMD would issue a compiler warning for untested return values?
>>>
>>> bool somefunc() { ... }
>>>
>>> void main() {
>>>   somefunc();//warning: untested return value
>>>   auto b = somefunc();//OK
>>> }
>>>
>>> Especially useful for C or OS functions returning error values or handles.
>>>
>>> L.
>>>
>>> PS. might even be worth a compiler error.
>>
>> I regularly use functions I don't need the return values of, so I wouldn't like this change.
>>
>> On the other hand, Walter might stop using printf() all over Phobos... :P
>> Nah, not worth it. Besides, the fact that functions like printf() have a return value is probably enough reason for Walter not to make such a change.
> 
> LOL, really?
> What does printf return? (what about writef?)

from http://www.cplusplus.com/ref/cstdio/printf.html (at bottom):
-----------
 *Return Value.*
  On success, the total number of characters printed is returned.
  On error, a negative number is returned.
-----------

I suppose it could be used if want to align the next output to a specific column without fixing all the fields to specific lengths.
Though the %n specifier could also be used for that[1].


[1] If you don't know what it does, don't worry. It's another obscure fact of printf(): %n accepts an int* that's filled with the number of characters printed so far. I believe it's main use is in format string exploits :P.

"Frits van Bommel" <fvbommel@REMwOVExCAPSs.nl> wrote in message news:eftv4g$2ueh$1@digitaldaemon.com...
> Lionello Lunesu wrote:
>> What would happen if DMD would issue a compiler warning for untested return values?
>>
>> bool somefunc() { ... }
>>
>> void main() {
>>   somefunc();//warning: untested return value
>>   auto b = somefunc();//OK
>> }
>>
>> Especially useful for C or OS functions returning error values or handles.
>>
>> L.
>>
>> PS. might even be worth a compiler error.
>
> I regularly use functions I don't need the return values of, so I wouldn't like this change.
>
> On the other hand, Walter might stop using printf() all over Phobos... :P Nah, not worth it. Besides, the fact that functions like printf() have a return value is probably enough reason for Walter not to make such a change.

Damn that printf :S

I actually use the printf in D quite a lot, but only because it's there. If writefln would be imported by default I'd use that instead.

L.

Lionello Lunesu wrote:

> I actually use the printf in D quite a lot, but only because it's there.If writefln would be imported by default I'd use that instead.

You're in good company then, the language's author agrees with you :-)

Seriously, it's in the wrong header. And it's pining for the fjords...

--anders

Anders F Björklund wrote:
> Seriously, it's in the wrong header. And it's pining for the fjords...

It just moved.

Walter Bright wrote:

> It just moved.

OK, so there might be a "import std.c.stdio;" to
insert in a couple of files to make them compile ?

Much better now than after the initial D release...
This should also help promote writef, which is good.

Thanks Walter,
--anders

Anders F Björklund wrote:
> Walter Bright wrote:
> 
>> It just moved.
> 
> OK, so there might be a "import std.c.stdio;" to
> insert in a couple of files to make them compile ?

I mean the parrot moved <g>.