Error code E0641

Attempted to cast to/from a pointer with an unknown kind.

Erroneous code example:

#![allow(unused)]
fn main() {
let b = 0 as *const _; // error
}
ⓘ

Type information must be provided if a pointer type being cast from/into another type which cannot be inferred:

#![allow(unused)]
fn main() {
// Creating a pointer from reference: type can be inferred
let a = &(String::from("Hello world!")) as *const _; // ok!

let b = 0 as *const i32; // ok!

let c: *const i32 = 0 as *const _; // ok!
}