Macro gen_params 

macro_rules! gen_params {
    (@ $builder:ident $key:literal: $value:expr $(, $($rest:tt)*)?) => { ... };
    (@ $builder:ident $key:literal?: $value:expr $(, $($rest:tt)*)?) => { ... };
    (@ $builder:ident $value:expr $(, $($rest:tt)*)?) => { ... };
    (@ $builder:ident $(,)?) => { ... };
    ($($args:tt)*) => { ... };
}