Type alias do not used in functions

[juev]

First, create new lib with type alias and function:

pub type OperationType = String;

lazy_static! {
    pub static ref OPERATION_TYPE_BUY: OperationType = String::from("Buy");
}

    pub fn limit_order(
        &self,
        account_id: &str,
        figi: &str,
        lots: i64,
        operation: OperationType,
        price: f64,
    ) -> Result<PlacedOrder> {
    ...
    }

Then, we use this crate in our program:

    let limit_order =
         rest_client.limit_order("", "BBG000BB88K4", 2, OPERATION_TYPE_BUY, 11 as f64)?;

OPERATION_TYPE_BUY has type OperationType, this type we expect in limit_order function, but we have error:

error[E0308]: mismatched types
  --> src/main.rs:38:57
   |
38 |          rest_client.limit_order("", "BBG000BB88K4", 2, OPERATION_TYPE_BUY, 11 as f64)?;
   |                                                         ^^^^^^^^^^^^^^^^^^
   |                                                         |
   |                                                         expected struct `std::string::String`, found struct `invest_openapi_rs_sdk::OPERATION_TYPE_BUY`
   |                                                         help: try using a conversion method: `OPERATION_TYPE_BUY.to_string()`

error: aborting due to previous error

If our function expect OperationType type, why rust asked me convert to String?

Meta

rustc --version --verbose:

$ rustc --version --verbose
rustc 1.46.0 (04488afe3 2020-08-24)
binary: rustc
commit-hash: 04488afe34512aa4c33566eb16d8c912a3ae04f9
commit-date: 2020-08-24
host: x86_64-apple-darwin
release: 1.46.0
LLVM version: 10.0

[Mark-Simulacrum]

This is, to some extent, a diagnostics bug (#17164).

The problem in this case is that lazy_static generates a static with a unique type, invest_openapi_rs_sdk::OPERATION_TYPE_BUY, not String (aliases to OperationType in this snippet). You can call clone() on the lazy_static unique type to get a copy of the String in it.

[juev]

@Mark-Simulacrum thank you!

If I use clone:

    let limit_order =
         rest_client.limit_order("", "BBG000BB88K4", 2, OPERATION_TYPE_BUY.clone(), 11 as f64)?;

it's work. But, its the same as

    let limit_order =
         rest_client.limit_order("", "BBG000BB88K4", 2, OPERATION_TYPE_BUY.to_string(), 11 as f64)?;

If I use type alias in function parameter, why it not the same unique type, what used in lazy_static?

[Mark-Simulacrum]

I don't quite follow your question.

lazy_static produces a static with an opaque type (it's nameable, but generally you shouldn't need to). That type is then not String, and provides only &String access through deref. You can read some more about this in the docs here https://docs.rs/lazy_static/1.4.0/lazy_static/#semantics

I would recommend reaching out on users.rust-lang.org for further help with this question; I'm going to close this as I think it's essentially a duplicate of the general problem with type aliases, #17164.