Macro slog::kv

macro_rules! kv {
    (@ $args_ready:expr; $k:expr => %$v:expr) => { ... };
    (@ $args_ready:expr; $k:expr => %$v:expr, $($args:tt)* ) => { ... };
    (@ $args_ready:expr; $k:expr => ?$v:expr) => { ... };
    (@ $args_ready:expr; $k:expr => ?$v:expr, $($args:tt)* ) => { ... };
    (@ $args_ready:expr; $k:expr => $v:expr) => { ... };
    (@ $args_ready:expr; $k:expr => $v:expr, $($args:tt)* ) => { ... };
    (@ $args_ready:expr; $kv:expr) => { ... };
    (@ $args_ready:expr; $kv:expr, $($args:tt)* ) => { ... };
    (@ $args_ready:expr; ) => { ... };
    (@ $args_ready:expr;, ) => { ... };
    ($($args:tt)*) => { ... };
}

Macro for build KV implementing type

You probably want to use o! or b! instead.