> Maybe you can use a wrapper type for the hot path which has an overriden =
> that is disabled.
Sounds like a nice workaround for now, thanks for the advice !
> But how to offer the feature otherwise... I don't know. An RFC is welcome.
So before i start writing an RFC, i would like to present my understanding (and
proposal) so you can smash me here before i start writing a silly RFC :D
Consider this trivial example:
type
X = object
s: string
proc `=copy`(x: var X, y: X): void =
x.s = "copy of " & y.s
proc consume(x: sink X) =
echo "Consumed: ", x.s
var x = X(s: "abcdefg")
consume(move(x))
echo "Unconsumed: ", x.s # < Could the compiler hint i'm using after move ?
Run
This prints this:
Consumed: abcdefg
Unconsumed:
Run
But i would like to enable a compiler hint, if possible
Btw i'm still trying to understand how the sink works (sorry i'm pretty new to
the language, coming from C++). Consider this slight variation:
type
X = object
s: string
proc `=copy`(x: var X, y: X) =
x.s = "copy of " & y.s
proc `=sink`(x: var X, y: X) =
`=destroy`(x)
wasMoved(x)
x.s = "moved " & y.s
proc consume(x: sink X) =
echo "Consumed: ", x.s
var x = X(s: "abcdefg")
consume(x)
Run
This surprisingly prints:
Consumed: copy of abcdefg
Run
the compiler seems unable to prove x is never read after the call to the proc
with sinked argument. To confirm this, i tried this other snippet, and it
doesn't work like i would expect:
type
X = object
s: string
proc `=copy`(x: var X, y: X) {.error.}
proc `=sink`(x: var X, y: X) =
`=destroy`(x)
wasMoved(x)
x.s = "moved " & y.s
proc consume(x: sink X) =
echo "Consumed: ", x.s
var x = X(s: "abcdefg")
consume(x)
Run
Produces:
Error: '=copy' is not available for type <X>; requires a copy because it's
not the last read of 'x'; routine: test
Run
