Macro params 

macro_rules! params {
    () => { ... };
    ($($key:ident => $value:expr),* $(,)?) => { ... };
    ($($value:expr),* $(,)?) => { ... };
}

let name = d; let age = 4; params!{a => 1, b => 2, c => name } —> generate Params::NamedParams{“a” : 1, “b”: 2, “c”: “d”} params!{ name, age } —> generate Params::QuestionParams{ vec![“d”, 4] }