Macro literal 

macro_rules! literal {
    ($lit:literal) => { ... };
    {
        $( $vis:vis $name:ident: $lit:literal; )+
    } => { ... };
}

Creates a literal value, or declares one or more named literal types.

Examples

// Creates an ad-hoc literal value.
foo().with_context(literal!("file not found"))?;

// Defines a list of typed literals.
literal!{
    pub NotFound: "file not found";
    pub InternalError: "internal error";
}
foo().with_context(NotFound)?;
foo().with_context_ty::<InternalError>()?;