Retrieval

Each registered object needs to be retrieved with the same lifetime that it was registered with.

For retrieval, the following functions are available on the [Registry]:

• Registry::transient::<T>()
• Registry::singleton::<T>()

The generic type parameter T is necessary to be specified, either on the function call or the assignee. It’s necessary to find which object to construct.

This is the example from the previous section:

#![allow(unused)]
extern crate ferrunix;
use ferrunix::{Transient, Registry};

pub struct CurrentCurrency(&'static str);
pub struct Config { currency: CurrentCurrency }

fn main() {
    let registry = Registry::empty();
    registry.register_transient(|| CurrentCurrency("USD"));
    registry
        .with_deps::<_, (Transient<CurrentCurrency>,)>() // Trailing comma required!
        .register_transient(|(currency,)| {
            Config {
                currency: currency.get(),
            }
        });

    // Construct a new config and currency.
    let config = registry.transient::<Config>().unwrap(); // <-- (1)
    let currency: CurrentCurrency = registry.transient().unwrap(); // <-- (2)

    // Assert that our retrieved object is actually what we expect.
    assert_eq!(config.currency.0, "USD");
    assert_eq!(currency.0, "USD");
}

At (1) the Registry::transient::<T>() function is used to construct a new Config. The generic type parameter T is directly specified at the function call.

However, at (2), the Rust compiler can infer the type T from the annotation on the left, and therefore, it’s not necessary to explicitly specify it.