Macro extract 

macro_rules! extract {
    ($expression:expr, $(
        $(|)? $( $pattern:pat_param )|+ $( if $guard: expr )? => $output:expr
    ),+ $(,)?) => { ... };
}

Returns the extracted value from the provided patterns.

Like a match expression, a pattern can be optionally followed by an if guard that has access to names bound by the pattern.

let array = [1, 2, 3];
let first = extract!(array, [el, ..] => el);
assert_eq!(first, Some(1));