Trait FromEnvVar

pub trait FromEnvVar:
    Debug
    + Sized
    + 'static {
    type Error: Error;

    // Required method
    fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>;

    // Provided methods
    fn from_env_var_or(
        env_var: &str,
        default: Self,
    ) -> Result<Self, FromEnvErr<Self::Error>> { ... }
    fn from_env_var_or_else(
        env_var: &str,
        default: impl FnOnce() -> Self,
    ) -> Result<Self, FromEnvErr<Self::Error>> { ... }
    fn from_env_var_or_default(
        env_var: &str,
    ) -> Result<Self, FromEnvErr<Self::Error>>
       where Self: Default { ... }
}

Trait for loading primitives from the environment. These are simple types that should correspond to a single environment variable. It has been implemented for common integer types, String, url::Url, tracing::Level, and std::time::Duration.

It aims to make FromEnv implementations easier to write, by providing a default implementation for common types.

Note on error types

FromEnv and FromEnvVar are often deeply nested. This means that error types are often nested as well. To avoid this, we use a single error type FromEnvVar that wraps an inner error type. This allows us to ensure that env-related errors (e.g. missing env vars) are not lost in the recursive structure of parsing errors. Environment errors are always at the top level, and should never be nested. Do not use FromEnvErr<T> as the Error associated type in FromEnv.

// Do not do this
impl FromEnv for MyType {
    type Error = FromEnvErr<MyTypeErr>;
}

// Instead do this:
impl FromEnv for MyType {
   type Error = MyTypeErr;
}

Implementing FromEnv

FromEnvVar is a trait for loading simple types from the environment. It represents a type that can be loaded from a single environment variable. It is similar to FromStr and will usually be using an existing FromStr impl.

// We can re-use the `FromStr` implementation for our `FromEnvVar` impl.
impl FromEnvVar for MyCoolType {
    type Error = <MyCoolType as FromStr>::Err;

    fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>
    {
        String::from_env_var(env_var).unwrap().parse().map_err(Into::into)
    }
}

Required Associated Types

type Error: Error

Error type produced when parsing the primitive.

Required Methods

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

Load the primitive from the environment at the given variable.

Provided Methods

fn from_env_var_or( env_var: &str, default: Self, ) -> Result<Self, FromEnvErr<Self::Error>>

Load the primitive from the environment at the given variable. If the variable is unset or empty, return the default value.

This function will return an error if the environment variable is set but cannot be parsed.

fn from_env_var_or_else( env_var: &str, default: impl FnOnce() -> Self, ) -> Result<Self, FromEnvErr<Self::Error>>

Load the primitive from the environment at the given variable. If the variable is unset or empty, call the provided function to get the default value.

This function will return an error if the environment variable is set but cannot be parsed.

fn from_env_var_or_default( env_var: &str, ) -> Result<Self, FromEnvErr<Self::Error>>

where Self: Default,

Load the primitive from the environment at the given variable. If the variable is unset or empty, return the value generated by Default::default.

This function will return an error if the environment variable is set but cannot be parsed.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementations on Foreign Types

impl FromEnvVar for bool

type Error = ParseBoolError

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for i8

type Error = <i8 as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for i16

type Error = <i16 as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for i32

type Error = <i32 as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for i64

type Error = <i64 as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for i128

type Error = <i128 as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for isize

type Error = <isize as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for u8

type Error = <u8 as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for u16

type Error = <u16 as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for u32

type Error = <u32 as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for u64

type Error = <u64 as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for u128

type Error = <u128 as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for usize

type Error = <usize as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for String

type Error = Infallible

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for Duration

type Error = ParseIntError

fn from_env_var(s: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for Address

type Error = <Address as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for Bytes

type Error = <Bytes as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for SignetEnvironmentConstants

type Error = <SignetEnvironmentConstants as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for HostConstants

type Error = <HostConstants as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for RollupConstants

type Error = <RollupConstants as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for SignetConstants

type Error = <SignetConstants as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for SignetSystemConstants

type Error = <SignetSystemConstants as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for Level

type Error = <Level as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for Url

type Error = <Url as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl FromEnvVar for U256

type Error = <Uint<256, 4> as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl<T> FromEnvVar for Option<T>

where T: FromEnvVar,

type Error = <T as FromEnvVar>::Error

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl<T> FromEnvVar for Box<T>

where T: FromEnvVar,

type Error = <T as FromEnvVar>::Error

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl<T> FromEnvVar for Arc<T>

where T: FromEnvVar,

type Error = <T as FromEnvVar>::Error

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl<T> FromEnvVar for Vec<T>

where T: From<String> + Debug + 'static,

type Error = Infallible

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl<T, U> FromEnvVar for Cow<'static, U>

where T: FromEnvVar, U: ToOwned<Owned = T> + Debug + ?Sized,

type Error = <T as FromEnvVar>::Error

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

impl<const N: usize> FromEnvVar for FixedBytes<N>

Available on crate feature alloy only.

type Error = <FixedBytes<N> as FromStr>::Err

fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>

Implementors