Macro consts 

macro_rules! consts {
    ($val: expr, $sym:ident $(,)?) => { ... };
    ($val: expr, $sym:ident: $_s:literal $(,)?) => { ... };
    ($val: expr, $sym:ident: $_s:literal, $($rest:tt)*) => { ... };
    ($val: expr, $sym:ident, $($rest:tt)*) => { ... };
}

A helper for symbols defined below. The macro’s job is to bind conveniently usable const items to the symbol names provided. For example, with symbol { a, b } you’d have sym::a and sym::b.