Macro stored_kind 

macro_rules! stored_kind {
    ($( $handle:ty => $variant:ident ),+ $(,)?) => { ... };
}

Implement ResourceKind for a kind stored in one Resource variant.

The kind is what the variant holds, so the kind’s type names the variant too. Every kind the graph stores is one of these: a variant carries nothing but its kind, and anything a kind needs beyond its handle — a texture view’s format — lives inside the kind itself rather than beside it in the variant.