4 ms·
Not entirely. Someone in the comments of the issue suggests to implement this with generics as: func PointerOf[T any](t T) *T { return &t } But that h
by majewsky 6y ago
Not entirely. Someone in the comments of the issue suggests to implement this with generics as:
func PointerOf[T any](t T) *T {
return &t
}
But that has a nasty gotcha:
func Process(x *int32) {
if (x != nil) {
fmt.Println(*x + 5);
}
}
func main() {
Process(nil); //ok
x := i32(5)
Process(&x); //ok
Process(PointerOf(5)); //BOOM: cannot use PointerOf(5) (value of
//type *int) as *int32 value in argument to Process
}
Go's type coercion is quite primitive. It strictly works inside-out (propagating types strictly upwards in the AST), with the only exception that a numeric literal can be coerced into a specific numeric type by considering the immediate parent in the AST. So when you have `func f(x int32)` and you call it as `f(5)`, the literal 5 gets coerced into int32 to match the context it appears in. (The same strategy is also applied to determine the type of a nil literal.)
However, in `Process(PointerOf(5))`, the immediate surrounding of the literal 5 (the PointerOf call) does not coerce the literal into a specific type, so it takes on its default type, int.
The proposal (or, to be exact, both proposals) avoids this gotcha by requiring a type to be stated explicitly.
Process(new(i32, 5));
Process(&i32(5));
- bbatha 6y agoYou can just write PointerOf(int32(5)) or PointerOf[int32](5). Or go could improve its type inference.