Macro impl_weights_wrapper 

macro_rules! impl_weights_wrapper {
    (
        $graph:ty,
        reduce N = $node_weight:tt,
        reduce E = $edge_weight:tt
        $(, <$($gens:tt),*>)?
        $(, |$(const $cgens:ident: $ity:ty),*|)?
    ) => { ... };
    (
        $graph:ty,
        reduce N = $node_weight:tt
        $(, <$($gens:tt),*>)?
        $(, |$(const $cgens:ident: $ity:ty),*|)?
    ) => { ... };
    (
        $graph:ty,
        reduce E = $edge_weight:tt
        $(, <$($gens:tt),*>)?
        $(, |$(const $cgens:ident: $ity:ty),*|)?
    ) => { ... };
    (
        $graph:ty
        $(, <$($gens:tt),*>)?
        $(, |$(const $cgens:ident: $ity:ty),*|)?
    ) => { ... };
}