On Sunday, 2 September 2018 at 05:14:58 UTC, Chris M. wrote:
Hopefully that was coherent. Again this is me for me to get my
thoughts out there, but also I'm interested in what other
people think about this.
Somewhat related, I was reading through this thread on why we
can't do ref variables and thought this was interesting. A lot of
these use cases could be prevented. I tacked my own comments on
with //**
https://forum.dlang.org/post/aqvtunmdqfkrsvzlg...@forum.dlang.org
struct S {
return ref int r;
}
//ref local variable/stack, Ticking timebomb
//compiler may refuse
//** nope, never accept this
void useRef(ref S input, int r) {
input.r = r; //** error
}
//should be good, right?
S useRef2(S input, return ref int r) { //Can declare @safe,
right???
input.r = r; //maybe, maybe not.
//** sure we can
return S;
}
//Shy should indirect care if it's local/stack or heap?
//** someone double-check my rationale here, but it should be fine
S indirect(return ref int r) {
return useRef2(S(), r);
}
//local variables completely okay to ref! Right?
//** Nope! Reject! indirect2() knows whatever receives the return
value can't outlive r
S indirect2() {
int r;
return useRef2(S(), r);
}
S someScope() {
int* pointer = new int(31); //i think that's right
int local = 127;
S s;
//reference to calling stack! (which may be destroyed now);
//Or worse it may silently work for a while
//** or the function never gets compiled
useRef(s, 99);
assert(s.r == 99);
return s;
s = useRef2(s, pointer); //or is it *pointer?
//** no clue what to say about this
one
assert(s.r == 31); //good so far if it passes correctly
return s; //good, heap allocated
s = useRef2(s, local); //** fine here, local outlives s
assert(s.r == 127); //good so far (still local)
return s; //Ticking timebomb!
//** but we reject it here
s = indirect(local); //** fine here, local outlives s
assert(s.r == 127); //good so far (still local)
return s; //timebomb!
//** reject again
s = indirect2(); //** never accepted in the first place
return s; //already destroyed! Unknown consequences!
}
