Function rustc_builtin_macros::deriving::generic::combine_substructure

source ยท 
pub(crate) fn combine_substructure(
    f: Box<dyn FnMut(&ExtCtxt<'_>, Span, &Substructure<'_>) -> BlockOrExpr + '_>,
) -> RefCell<Box<dyn FnMut(&ExtCtxt<'_>, Span, &Substructure<'_>) -> BlockOrExpr + '_>>