Type Definition rustc_builtin_macros::deriving::generic::CombineSubstructureFunc

type CombineSubstructureFunc<'a> = Box<dyn FnMut(&mut ExtCtxt<'_>, Span, &Substructure<'_>) -> P<Expr> + 'a>;

Combine the values of all the fields together. The last argument is all the fields of all the structures.