Struct smart_config::fallback::Manual

pub struct Manual { /* private fields */ }

Custom fallback value provider.

Use cases

This provider is useful when configuration parameter deserialization logic is hard to express using conventional methods, such as:

• Composite configuration parameters that rely on several environment variables. In this case, you can use the getter closure to access variables via Env and combine them into a single value.
• Configuration values that need additional validation to make the configuration object correct by construction. For example, if your config has an optional field, which should be None either if it’s absent or set to the "unset" value, you can first get it via Env, and then only provide value if it’s not equal to "unset". You can think of it as a filter or map function in this case.

Examples

use smart_config::{
    fallback, testing, value::{ValueOrigin, WithOrigin},
    DescribeConfig, DeserializeConfig,
};

// Value source combining two env variables. It usually makes sense to split off
// the definition like this so that it's more readable.
const COMBINED_VARS: &'static dyn fallback::FallbackSource =
    &fallback::Manual::new("$TEST_ENV - $TEST_NETWORK", || {
        let env = fallback::Env("TEST_ENV").get_raw()?;
        let network = fallback::Env("TEST_NETWORK").get_raw()?;
        let origin = Arc::new(ValueOrigin::EnvVars);
        Some(WithOrigin::new(format!("{env} - {network}").into(), origin))
    });

#[derive(DescribeConfig, DeserializeConfig)]
struct TestConfig {
    #[config(default_t = "app".into(), fallback = COMBINED_VARS)]
    app: String,
}

let config: TestConfig = testing::Tester::default()
    .set_env("TEST_ENV", "stage")
    .set_env("TEST_NETWORK", "goerli")
    .test(smart_config::config!())?;
assert_eq!(config.app, "stage - goerli");

Implementations

impl Manual

pub const fn new( description: &'static str, getter: fn() -> Option<WithOrigin>, ) -> Self

Creates a provider with the specified human-readable description and a getter function.

Trait Implementations

impl Debug for Manual

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for Manual

fn fmt(&self, formatter: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl FallbackSource for Manual

fn provide_value(&self) -> Option<WithOrigin>

Potentially provides a value for the param.