You have options. Given Superset struct A, some other struct B that happens to have a subset of A’s fields, and some function foo which takes an argument of ty

You have options. Given Superset struct A, some other struct B that happens to have a subset of A’s fields, and some function foo which takes an argument of type B, you could 1) implement From<A> for B, and use that to convert instances of A when you want to call foo. This would probably involve some copying and/or allocation. 2) back up and turn foo into something that takes a trait argument instead. Now instead of taking instances of A, what it needs struct to provide is defined by a trait, which you can provide implementations of for both A and B. Now you can pass either to foo. 3) potentially, depending on the layout of structs, create a union and do some type punning to convert between them. this requires unsafe and you’d better be right about the struct layouts. 4) just make foo take a tagged union of the two structs. this isn’t unsafe but has different storage tradeoffs. also foo would need to handle each case separately. 5) find some other way to skin this cat. there’s plenty #2 would be idiomatic in most circumstances I think?