Re: undefined compound chaining behavior

[Hossein Sajjadi]

but such an expression results in undefined behavior

On 6/6/14, Rik <address@hidden> wrote:
> On 06/06/2014 08:06 AM, address@hidden wrote:
>> Message: 5
>> Date: Fri, 6 Jun 2014 17:20:08 +0330
>> From: Hossein Sajjadi <address@hidden>
>> To: address@hidden
>> Subject: chaining compound assignment results in undefined behavior
>> Message-ID:
>>      <address@hidden>
>> Content-Type: text/plain; charset=UTF-8
>>
>> Hi
>>
>> There is a problem with chaining compound assignment.
>> For example the expression a=1;a+=a+=4 will result 10.
>> I think such a behavior is borrowed from C language but this behavior
>> is known as "undefined behavior".
>>  This issue have been resolven in Java.
>>  Java language guarantees that the operands of operators appear
>> to be evaluated in a specific evaluation order , namely, from left to
>> right. ?15.7
>> Other specifications about evaluation of expressions are in
>> "The Java? Language Specification"
>>
>>  also this approach is followed by c# language
>>  so result of above expression in Java is 6
>
> I don't think we need to do anything here.  First, code should
> self-documenting and easy to understand.  When I first looked at the
> statement I couldn't figure out what the intent was, and so I'm not
> surprised that the compiler also has a hard time deciding what to do.  So,
> I would suggest that rather than introduce complexities in to the parser,
> the programmer should simply write what they mean.
>
> If the programmer wants 6 as an answer, then code
> a = 1; a += a; a+= 4
>
> If the programmer wants 10 as an answer, then code
> a = 1; a +=4; a += a
>
> I tried the example in C++ and the result with the gcc compiler is 10 so
> I'm perfectly happy to define the behavior that multiple in-place operators
> are evaluated in a specific evaluation order which happens to be "right to
> left".
>
> Cheers,
> Rik
>