Bug 18508 – Using statement without effect should error

cat << EOF | dmd -c -o- - int f(int a){ return a; } void main() { int a; a=f(0),f(1); assert(a==1); } EOF It already errors for cat << EOF | dmd -c -o- - int f(int a){ return a; } void main() { int a; a=0,1; assert(a==1); } EOF

I'm not sure what is and isn't supposed to be legal with the comma operator now, but if the issue is that the statement has no effect, then there isn't necessarily a bug here, because f isn't pure. Yes, _we_ can see that f has no effect, but the compiler doesn't look past the signature. Now, I slapped pure on f to see what would happen, and that still doesn't produce an error, so there probably is a bug if your example has pure on f, but as-is, I'm not sure that it actually shows a bug.

It is supposed to be illegal to use the result of a comma expression. See here: https://dlang.org/spec/expression.html#expression

Yep, no statement without effect in the example. Even pure function can still throw exception, which is effect too.