https://d.puremagic.com/issues/show_bug.cgi?id=12028

           Summary: Disallow side effects in asserts
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2014-01-29 08:25:00 PST ---
I suggest to statically disallow code like this, that is to disallow side
effects in assert(), that are source of bugs (because the code can act
differently in release mode):


int foo(ref int y) pure nothrow {
    return y++;
}
void main() {
    int x;
    assert(++x);
    assert(foo(x));
}

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Andrej Mitrovic <andrej.mitrovich@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |andrej.mitrovich@gmail.com


--- Comment #1 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2014-01-30 01:49:47 PST ---
It might be controversial, however I do remember someone actually running into this bug in #d last year.

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Dylan Knutson <tcdknutson@gmail.com> changed:

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                 CC|                            |tcdknutson@gmail.com


--- Comment #2 from Dylan Knutson <tcdknutson@gmail.com> 2014-02-03 14:01:09 PST ---
Andrej, I believe that was me! It would have been nice to have that code checked for side effects in assert statements. I'm in support of this enhancement request.

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--- Comment #3 from bearophile_hugs@eml.cc 2014-02-03 14:33:11 PST ---
A discussion thread: http://forum.dlang.org/thread/yzopesnnlgidhelsrrci@forum.dlang.org


A problem raised by Brad Roberts:

> I have one semi-large code base where I validate the locking semantics by adding assert(!lock.try_acquire)'s.  That's clearly a side effect, but also clearly should never have one if the code is correct.


And an answer by Marco Leise:

> Basically lock.try_acquire is pure when it returns false, and if not, the program is terminated anyways so it doesn't make a difference.

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