No safe way to get a raw ptr to an uninitialized variable

[sp3d]

I would argue that the following code is safe (rustc presently disagrees: "error: use of possibly uninitialized variable: a") and there should be a way to write it:

fn main(){
    let a: int;
    let b: *int = &a;
}

The analysis is correct in that obtaining an &-ptr to an uninitialized variable allows for unsafety, but there should be a way to get the address of a variable as a raw-ptr without needing a guarantee that a valid value lives at that address.

[thestinger]

I don't really think this is necessary. There's the uninit function for declaring an uninitialized variable. The ability to create raw pointers without unsafe is more of a novelty than something useful (real pointer arithmetic via offset is unsafe anyway).

[sp3d]

It would still be nice to have this possible without an unsafe block, but it didn't come to mind that uninit() would work as a trapdoor here. Oversafety is less of a problem than inability to express immutable circular references.

It would be nice if we explicitly stated in docs that the reason to use uninit is to convince the compiler that a variable has been initialized without actually doing the work to initialize it (which is, of course, unsafe in general, unlike the suggested feature).

[thestinger]

The &a operation here returns &int, not *int, which is then coerced to a raw pointer. It's not clear how this could actually be implemented. Regardless, it's a fundamental language change and would need to go through the RFC process. It's not a missing low-level capacity since mem::uninitialized provides the functionality.