More from C++ Now 2014

[qznc via Digitalmars-d]

On Monday, 19 May 2014 at 08:20:54 UTC, Namespace wrote:
> On Sunday, 18 May 2014 at 22:29:04 UTC, bearophile wrote:
>>> "Undefined Behavior in C++; what is it, and why should I 
>>> care":
>>> https://github.com/boostcon/cppnow_presentations_2014/blob/master/files/Undefined-Behavior.pdf?raw=true
>>> This reminds us to remove as much undefined behavior as 
>>> possible from D.
>>
>> Fixing some of those problems will break some D code. An 
>> example from the slides pack:
>>
>> void main() {
>>    import std.stdio;
>>    auto arr = [0, 2, 4, 6, 8];
>>    int i = 1;
>>    writeln(i + arr[++i] + arr[i++]);
>> }
> dmd is right, so ldc has probably a bug.
> i is 1
> ++i is 2 -> arr[2] is 4
> i++ is still 2 -> arr[2] is 4
> 1 + 4 + 4 = 9

Addition does not imply an order in D, does it? So, the following 
lines should be equivalent:

writeln(i + arr[++i] + arr[i++]);
writeln(arr[++i] + i + arr[i++]);
writeln(arr[i++] + i + arr[++i]);
writeln(i + arr[i++] + arr[++i]);

Your reasoning step "is still 2" is inapplicable when there is no 
order.