Macro nom::lib::std::prelude::v1::v1::option_env

macro_rules! option_env {
    ($ name : expr) => { ... };
    ($ name : expr,) => { ... };
}

Optionally inspects an environment variable at compile time.

If the named environment variable is present at compile time, this will expand into an expression of type Option<&'static str> whose value is Some of the value of the environment variable. If the environment variable is not present, then this will expand to None. See Option<T> for more information on this type.

A compile time error is never emitted when using this macro regardless of whether the environment variable is present or not.

Examples

let key: Option<&'static str> = option_env!("SECRET_KEY");
println!("the secret key might be: {:?}", key);