Macro named_args 

macro_rules! named_args {
    ($($key:expr => $value:expr,)+) => { ... };
    ($($key:expr => $value:expr),*) => { ... };
}

Builds a named argument collection for a query with $name parameters:

let args = named_args! { "id" => id, "label" => "urgent".to_string() };

Builds a HashMap<&str, ValueOpt>, with a trailing comma allowed.