Rust Error E0605: Invalid Cast

Understanding Rust Error E0605

Rust Error E0605 occurs when an invalid cast is attempted in the code. In Rust, only primitive types can be cast into each other using the 'as' keyword. Examples of primitive types are integers (u8, i32, etc.), floating-point numbers (f32, f64), and pointers to these types (*const T).

Erroneous Code Examples

In these examples, we will demonstrate a few instances where Rust Error E0605 is produced due to invalid casting:

let x = 0u8;
x as Vec<u8>; // error: non-primitive cast: `u8` as `std::vec::Vec<u8>`
let v = core::ptr::null::<u8>(); // So here, `v` is a `*const u8`.
v as &u8; // error: non-primitive cast: `*const u8` as `&u8`

Valid Cast Examples

When casting between primitive types, the Rust compiler will not produce Error E0605. Here are some examples of valid casting:

let x = 0u8;
x as u32; // ok!
let v = core::ptr::null::<u8>();
v as *const i8; // ok!

How to Fix Rust Error E0605

To fix Rust Error E0605, you must ensure that you are only casting between compatible primitive types. If you need to convert between non-primitive types such as structs, enums, and other custom data types, you will need to use a different approach. This might include implementing custom conversion methods, using traits like `From` and `Into`, or applying a library supporting the required conversion.

For more information on how casting works in Rust and how to avoid Rust Error E0605, study the relevant sections in The Nomicon and The Rust Reference provided in the recommended reading.