Using a struct from another module in a new module

问题

The following code doesn't compile, because it says that requests is not defined when I try to use it in the operations module.

I think this maybe has something to do with importing modules maybe, but I'm really new to rust and don't understand. I thought I could just do module::struct and as long as the struct was public I would be able to access it.

Can someone explain why this doesn't work, and how to make this work?

pub mod vehicles {
    pub struct Vehicle {
        _vehicle_id: u64,
        _capacity: u32,
    }

    impl Vehicle {
        pub fn new(id: u64, cap: u32) -> Vehicle {
            Vehicle {
                _vehicle_id: id,
                _capacity: cap,
            }
        }

        pub fn get_id(&self) -> u64 {
            self._vehicle_id
        }

        pub fn get_capacity(&self) -> u32 {
            self._capacity
        }
    }
}

mod requests {
    pub struct Request {
        _request_id: u64,
        _request_time: i64,
        _origin: u64,
        _destination: u64,
        _assigned: bool,
    }

    impl Request {
        pub fn new(id: u64, time: i64, origin: u64, dest: u64) -> Request {
            Request {
                _request_id: id,
                _request_time: time,
                _origin: origin,
                _destination: dest,
                _assigned: false,
            }
        }

        pub fn get_id(&self) -> u64 {
            self._request_id
        }

        pub fn get_request_time(&self) -> i64 {
            self._request_time
        }

        pub fn get_origin(&self) -> u64 {
            self._origin
        }

        pub fn get_destination(&self) -> u64 {
            self._destination
        }

        pub fn is_assigned(&self) -> bool {
            self._assigned
        }
    }
}

pub mod operations {
    #[derive(Clone, Copy)]
    pub enum OperationType {
        PICKUP,
        DROPOFF,
    }
    pub struct Operation {
        _request: requests::Request,
        _location: u64,
        _operation_type: OperationType,
        _expected_time: i64,
    }
    impl Operation {
        pub fn new(request: requests::Request, optype: OperationType, location: u64, time: i64) -> Self {
            Self {
                _request: request,
                _operation_type: optype,
                _location: location,
                _expected_time: time,
            }
        }
        pub fn get_location(&self) -> u64 {
            self._location
        }
        pub fn get_request(&self) -> &requests::Request {
            &self._request
        }
        pub fn get_type(&self) -> OperationType {
            self._operation_type
        }
        pub fn get_expected_time(&self) -> i64 {
            self._expected_time
        }
    }
}

回答1:

Since Rust 2018, you must use crate keyword, add use crate::requests; somewhere (generally on the top) in the module where you want use requests.

See, the relevant module section in the book.

来源：https://stackoverflow.com/questions/60021688/using-a-struct-from-another-module-in-a-new-module