Macro select 

macro_rules! select {
    (@build [$($arms:tt)*] $val:ident = $rx:expr => $body:expr, $($rest:tt)*) => { ... };
    (@build [$($arms:tt)*] timeout($dur:expr) => $body:expr $(,)?) => { ... };
    (@build [$($arms:tt)*]) => { ... };
    ($($tokens:tt)*) => { ... };
}

Select over multiple channel operations with optional timeout.

Syntax

camber::select! {
    val = rx1 => expr1,
    val = rx2 => expr2,
    timeout(duration) => expr3,
}

Each recv arm binds the received Result<T, RuntimeError> to val. The timeout arm fires if no channel is ready within the given Duration. All arms must produce the same type.