Macro selector 

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

Compile-time-expanded Selector builder. Equivalent to a sequence of .eq(key, value) calls:

let s = selector!(phase = "ann_query", k = "100");
// expands to:
let s = Selector::new().eq("phase", "ann_query").eq("k", "100");

Only = is supported — callers needing !=, ~=, ?, or !? use the builder API directly or Selector::parse.