Macro fields

macro_rules! fields {
    (@__entry $key:ident) => { ... };
    (@__entry $key:ident = $expr:expr) => { ... };
    (@__entry $key:literal = $expr:expr) => { ... };
    (@__entry [$key:expr] = $expr:expr) => { ... };
    () => { ... };
    ( $(
        $name:tt $(= $expr:expr)?
    ),+ $(,)? ) => { ... };
}

Creates a new Fields instance with the given fields.

The fields are specified as a comma-separated list of key = value pairs. Field values can be any type that implements the ToValue trait.