Macro delegate_impls_to_as_ref 

macro_rules! delegate_impls_to_as_ref {
    (for $target:ty => $($trait:ident $(where [$($generics:tt)*])? {  $(fn $func:ident$(<$($generic_arg:ident: $generic_arg_ty:path),*>)?(&self, $($arg:ident: $argty:ty),*) -> $ret:path;)* })* ) => { ... };
}

A macro that delegates trait implementations to the as_ref function of the type.

Used to implement provider traits.