Macro namespaces 

macro_rules! namespaces {
    (@accessors [$($field:ident),+]) => { ... };
    (@accessors [$($field:ident),+]
        $(#[$meta:meta])* $name:ident: $ns:path { $($to:ident: $from:ident),+ $(,)? }
        $(, $($rest:tt)*)?
    ) => { ... };
    (@accessors [$($field:ident),+]
        $(#[$meta:meta])* $name:ident: $ns:path
        $(, $($rest:tt)*)?
    ) => { ... };
    ($($field:ident),+; $($accessors:tt)*) => { ... };
}

Generates a client’s namespace accessors: each clones the listed client fields into the same-named fields of its namespace struct.

The invocation starts with the fields every namespace takes, then lists one accessor per namespace, with its attributes. An accessor may instead name its own field mapping, name: Type { to: from, .. }, which clones self.from into Type::to. The namespace structs stay declared by hand, since their paths are public API.

#[derive(Clone)]
pub struct Http;

pub struct Markets {
    http_client: Http,
}

pub struct Pnl {
    http_client: Http,
}

pub struct Client {
    http_client: Http,
    pnl_http_client: Http,
}

impl Client {
    polyoxide_core::namespaces! { http_client;
        /// The markets namespace.
        markets: Markets,
        /// The PnL namespace, on its own host.
        pnl: Pnl { http_client: pnl_http_client },
    }
}