# Error code E0433

An undeclared crate, module, or type was used.

Erroneous code example:

    #![allow(unused)]
    fn main() {
    let map = HashMap::new();
    // error: failed to resolve: use of undeclared type `HashMap`
    }

Please verify you didn't misspell the type/module's name or that you didn't forget to import it:

    #![allow(unused)]
    fn main() {
    use std::collections::HashMap; // HashMap has been imported.
    let map: HashMap<u32, u32> = HashMap::new(); // So it can be used!
    }

If you've expected to use a crate name:

    #![allow(unused)]
    fn main() {
    use ferris_wheel::BigO;
    // error: failed to resolve: use of undeclared crate or module `ferris_wheel`
    }

Make sure the crate has been added as a dependency in `Cargo.toml`.

To use a module from your current crate, add the `crate::` prefix to the path.