https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97288
--- Comment #1 from Amir Kirsh <kirshamir at gmail dot com> ---
For user defined type this behavior might be ok, as the order of evaluation of
parameters is not defined, however this behavior is reflected also for
primitive types:
int main() {
int a {5};
(a += 1) += a;
std::cout << a << std::endl;
}
gcc gives a warning:
warning: operation on 'a' may be undefined [-Wsequence-point]
5 | (a += 1) += a;
| ~~~^~~~~
<source>:5:8: warning: operation on 'a' may be undefined [-Wsequence-point]
and result is 12.
Though based on C++17 sequencing rules for assignment, seems that the operation
shall be valid (no warning) and result with 11.
http://eel.is/c++draft/expr.ass#1
Code: https://godbolt.org/z/G1Kahh
