On Tuesday, 23 July 2019 at 00:54:08 UTC, aliak wrote:
On Tuesday, 23 July 2019 at 00:36:49 UTC, Exil wrote:
auto ref get(T)(W!T value) {
return value.front;
}
You're returning a reference to a temporary that gets deleted
at the end of the function's scope. The "auto ref" here will
be a "ref".
..... oh ... shit.... you're right.
Ok so this was minimized from this:
const config = Config.ghApp(ghDomain)
.orElseThrow!(() => new Exception(
"could not find config for domain
'%s'".format(ghDomain)
));
Where Config.ghApp return an Optional!GhApp, and orElseThrow
checks if a range has is not empty and returns front. The front
in Optional is defined as the front above...
So is that an incorrect idiom to use when writing a library
then? I pretty sure I've seen it in phobos too.
Slapping return on the function also fixes it. Is that the
correct way to write a .front?
Thanks!
Yes you can use "return". It basically tells the compiler that
the function or method returns something that is referenced by a
passed in parameter so to keep it alive.
https://dlang.org/spec/function.html#return-ref-parameters
Your orElseThrow() probably shouldn't be taking in a copy though.
That's the catch, then you can't use it in a UFCS chain like you
are using now. Using "return" is not an ideal fix, as it is still
going to be calling the destructor on the object. So you might
run into an issue somewhere. It just so happens to generate
assembly that works though I guess when there is no destructor.
