Macro env_flags

macro_rules! env_flags {
    ($(#[$attr:meta])* $key:ident : $ty:ty; $($rem:tt)*) => { ... };
    ($(#[$attr:meta])* pub $key:ident : $ty:ty; $($rem:tt)*) => { ... };
    ($(#[$attr:meta])* pub ($($vis:tt)+) $key:ident : $ty:ty; $($rem:tt)*) => { ... };
    ($(#[$attr:meta])* $key:ident : $ty:ty = $default:expr; $($rem:tt)*) => { ... };
    ($(#[$attr:meta])* pub $key:ident : $ty:ty = $default:expr; $($rem:tt)*) => { ... };
    ($(#[$attr:meta])* pub ($($vis:tt)+) $key:ident : $ty:ty = $default:expr; $($rem:tt)*) => { ... };
    ($(#[$attr:meta])* $key:ident : $ty:ty, $parse_fn:expr; $($rem:tt)*) => { ... };
    ($(#[$attr:meta])* pub $key:ident : $ty:ty, $parse_fn:expr; $($rem:tt)*) => { ... };
    ($(#[$attr:meta])* pub ($($vis:tt)+) $key:ident : $ty:ty, $parse_fn:expr; $($rem:tt)*) => { ... };
    ($(#[$attr:meta])* $key:ident : $ty:ty = $default:expr, $parse_fn:expr; $($rem:tt)*) => { ... };
    ($(#[$attr:meta])* pub $key:ident : $ty:ty = $default:expr, $parse_fn:expr; $($rem:tt)*) => { ... };
    ($(#[$attr:meta])* pub ($($vis:tt)+) $key:ident : $ty:ty = $default:expr, $parse_fn:expr; $($rem:tt)*) => { ... };
    () => { ... };
}

Declare environment variables with optional defaults and parsing functions.

Values are static and lazily evaluated once the first time they are dereferenced.

See the module-level documents for examples.