On 2020-03-28 00:40, Adam D. Ruppe wrote:
> It used to be this way! D had a custom exception mechanism (on linux, on
> Windows it used SEH which works very well) that was quite lightweight,
> but it got killed in the name of C++ compatibility :(
Funny thing. There's a C++ proposal by Herb Sutter, "Zero-overhead
deterministic exceptions: Throwing values" [1]. Which more or less
lowers the current syntax used for exception to something similar to
return codes.
Existing C++ code like this (which can not afford to use table based
exceptions):
expected<int, errc> safe_divide(int i, int j) {
if(j==0)
return unexpected(arithmetic_errc::divide_by_zero);
if(i==INT_MIN&&j==-1)
return unexpected(arithmetic_errc::integer_divide_overflows);
if(i%j!=0)
return unexpected(arithmetic_errc::not_integer_division);
else return i / j;
}
expected<double, errc> caller(double i, double j, double k) {
auto q = safe_divide(j, k);
if (q) return i + *q;
else return q;
}
Can with the new proposal be expressed like this:
int safe_divide(int i, int j) throws {
if(j==0)
throw arithmetic_errc::divide_by_zero;
if(i==INT_MIN&&j==-1)
throw arithmetic_errc::integer_divide_overflows;
if(i%j!=0)
throw arithmetic_errc::not_integer_division;
else return i / j;
}
double caller(double i, double j, double k) throws {
return i + safe_divide(j, k);
}
Which are more or less lowered to code similar as the original example.
If we want to stay compatible with C++ exception handling, we need to
implement this :). Although we currently don't support any other
features added after C++98.
[1] http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0709r0.pdf
--
/Jacob Carlborg