Remove the Error bound from get_or_try_insert_with method

[tatsuya6502]

In #23, the trait bounds for E was changed from Box<dyn Error + ...> to Error + ....

Current

use std::error::Error;

pub fn get_or_try_insert_with<F, E>(&self, key: K, init: F) -> Result<V, Arc<E>>
where
    F: FnOnce() -> Result<V, E>,
    E: Error + Send + Sync + 'static,

This pull request removes the Error bound from E.

After

pub fn get_or_try_insert_with<F, E>(&self, key: K, init: F) -> Result<V, Arc<E>>
where
    F: FnOnce() -> Result<V, E>,
    E: Send + Sync + 'static,

We are doing this because having Error is not necessary and too strict. For example, the following code will not compile with the current bounds, because anyhow::Error does not implement std::error::Error trait.

// Cargo.toml
// [dependencies]
// anyhow = "1"

use moka::sync::Cache;

fn main() -> anyhow::Result<()> {
    let cache: Cache<i32, i32> = Cache::new(1024);

    let _ = cache
        // The return type of the init closure is Result<i32, anyhow::Error>.
        // Note that anyhow::Error does not implement std::error::Error.
        .get_or_try_insert_with(0, || Err(anyhow::anyhow!("Always fail")))
        // Wrap Arc<anyhow::Error> with anyhow::Error.
        .map_err(|e| anyhow::anyhow!(e))?;
    Ok(())
}

error[E0277]: the trait bound `anyhow::Error: std::error::Error` is not satisfied
  --> src/bin/main1.rs:13:10
   |
13 |         .get_or_try_insert_with(0, || Err(anyhow::anyhow!("Always fail")))
   |          ^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `anyhow::Error`

error: aborting due to previous error

Removing the Error bound resolves the compile error.

[tatsuya6502]

Merging