On Thursday, 12 October 2017 at 15:37:23 UTC, John Burton wrote:
C++ compilers can and do perform such optimizations so I was
wondering if assert in D could cause such behavior according to
the spec.
In the context of ISO-C++ it is meaningless to reason about the
"actual behavior" of a non-conforming program ("start WW III"
etc.). You may find details here:
<http://en.cppreference.com/w/cpp/language/ub>
As standard oriented C++ (or C or FORTRAN) programmers we avoid
undefined behavior not because we would want to prevent WW III,
but because we want to write and reason about conforming code
only.
IIRC C++'s assert is defined in the ISO-C standard. There we can
read:
"The assert macro puts diagnostic tests into programs; it expands
to a void expression. When it is executed, if expression (which
shall have a scalar type) is false (that is, compares equal to
0), the assert macro writes information about the particular call
that failed [...] on the standard error stream in an
implementation-defined format). It then calls the abort function."
So in C/C++
---
int main ()
{
assert (0);
return 0;
}
---
is a perfectly valid (conforming) program.
D ist not standardized (yet) hence there is no such thing as a
"standard conforming D implementation" or a "standard conforming
D program". The D documentation is simply the manual of a set of
programs (compiler, tools) which may or may not be correctly be
described therin. According to
<https://dlang.org/spec/contracts.html> the program
---
void main ()
{
assert (false);
}
---
qualifies as "invalid, and therefore has undefined behaviour." A
statement, which makes no sense to me. Either it is a "debugging
aid", that implies defined behavior, or it is undefined behavior,
then assert (false) cannot aid debugging.
