Understanding Rust Error E0607: A Cast Between Thin and Fat Pointers
Rust Error E0607: A Cast Between Thin and Fat Pointers
Rust Error E0607 occurs when a cast is attempted between a thin pointer and a fat pointer. In the error message, you'll often see an erroneous code example that helps to identify the error. Let's explore what thin and fat pointers are, why this error occurs, and how to fix it.
Thin Pointers vs Fat Pointers
Thin pointers are simple pointers that refer to a memory address. They contain no additional information besides the memory address.
Fat pointers, on the other hand, reference Dynamically Sized Types (DSTs), which do not have a statically known size. Therefore, they require additional information to be held by pointers. Two common examples of DSTs are slices and trait objects. In the case of slices, the fat pointer would store the size of the slice.
Rust Error E0607 Example
Let's take a look at an example of the erroneous code that triggers Rust Error E0607:
```rust
#![allow(unused)]
fn main() {
let v = core::ptr::null::<u8>();
v as *const [u8];
}
```In this example, the error occurs because a direct cast between a thin pointer and a fat pointer is attempted at the line 'v as *const [u8];'.
Fixing Rust Error E0607
To fix Rust Error E0607, avoid casting directly between thin and fat pointers. Instead, consider alternative methods to achieve the desired result. One such method is to use slices or other mechanisms that provide size information.
Here's an example of corrected code that avoids Rust Error E0607:
```rust
#![allow(unused)]
fn main() {
let v = core::ptr::null::<u8>();
let slice: &[u8] = unsafe { std::slice::from_raw_parts(v, 5) };
let fat_ptr = slice as *const [u8];
}
```In this corrected code, the pointer 'v' is converted to a slice with 'std::slice::from_raw_parts(v, 5)' before being cast to a fat pointer. This gives the size information needed for the fat pointer, avoiding Rust Error E0607.