Macro dispatch 

macro_rules! dispatch {
    ($client:expr, $update:expr, $( $pattern:tt )+ ) => { ... };
}

Route a crate::update::Update to the first matching arm.

Syntax

dispatch!(client, update,
    VariantName(binding) [if guard] => { body },
    ...
    [_ => { fallback }]
);

• client — a layer_client::Client (available inside every arm body)
• update — the Update value to dispatch
• Each arm mirrors a variant of crate::update::Update
• Guards (if expr) are optional
• A catch-all _ => {} arm is optional but recommended to avoid warnings