Re: More from C++ Now 2014
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++]);
}
It gives different results in dmd and ldc2:
...dmd -wi -run temp.d
9
...ldmd2 -wi -run temp.d
10
Hopefully no one writes code like that, but this situation
can't be accepted in a language that tries to be safer and
better than C/C++.
Bye,
bearophile
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
Re: More from C++ Now 2014
On Sunday, 18 May 2014 at 18:03:26 UTC, bearophile wrote: Some more slides pack from C++ Now 2014: 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. Mach7: The Design and Evolution of a Pattern Matching Library for C++, by Bjarne Stroustrup and others: https://github.com/boostcon/cppnow_presentations_2014/blob/master/files/open-pattern-matching.pdf?raw=true This could be a start point to add pattern matching in D, or to discuss. Pattern matching requires lot of compiler support and some specific syntax. Iterators May Stay: https://github.com/boostcon/cppnow_presentations_2014/blob/master/files/CppNow2014Ranges.pdf?raw=true This looks like an answer to the Iterators must go talk. There are many comments about D ranges and some slides about Phobos. Ownership of Memory in C++: https://github.com/boostcon/cppnow_presentations_2014/blob/master/files/ownership_of_memory.pdf?raw=true This reminds us to not use linked lists. Arrays or arrays of smart pointers are good. Why aren't Reddit people discussing on each of those? :-) Bye, bearophile Two another interesting ones are My Thoughts on Large Code Base Change Ripple Management in C++ https://github.com/boostcon/cppnow_presentations_2014/blob/master/files/change_ripple.pdf?raw=true Keynote: Beware of C++ https://github.com/boostcon/cppnow_presentations_2014/blob/master/files/Josuttis_C++Now_140515_handouts.pdf?raw=true As they highlighting the issues C++ complexity has vs other languages, and the corresponding impact in the community. -- Paulo
Re: More from C++ Now 2014
Namespace: dmd is right, so ldc has probably a bug. I think D specs don't yet require a defined behaviour for that code, so I think both outputs are correct. Bye, bearophile
Re: More from C++ Now 2014
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.
Re: More from C++ Now 2014
On Monday, 19 May 2014 at 09:26:23 UTC, qznc wrote:
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.
Actually, he got that part right. i++ will always be 2, as it's
only incremented after the statement is done. It took me a
minute to realize how the ldc result was even possible: it's
because the result depends on whether the pre-increment ++i is
done before the entire statement is evaluated, so both i and ++i
are 2, or between evaluating i and arr[++i], so i is 1 and ++i is
2. dmd and ldc apparently do the pre-increment at different
times, hence undefined behavior.
Re: More from C++ Now 2014
On 05/18/2014 11:03 AM, bearophile wrote: Some more slides pack from C++ Now 2014: For those of us who are in the Bay Area, we will have a trip report: http://www.meetup.com/SFBay-Association-of-C-C-Users/events/179180452/ Ali
Re: More from C++ Now 2014
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++]);
}
It gives different results in dmd and ldc2:
...dmd -wi -run temp.d
9
...ldmd2 -wi -run temp.d
10
Hopefully no one writes code like that, but this situation can't
be accepted in a language that tries to be safer and better than
C/C++.
Bye,
bearophile
