Having a

  struct Context {
    a: u32,
    b: bool,
    c: String
  }

  struct SubContext1 {
    a: u32,
    b: bool
  }

  struct SubContext2 {
    a: u32,
    c: String
  }

How can the FromContext implementations be written? Seems like they take and return a reference, and there doesn't seem to be a way to satisfy the borrow checker.

Maybe FromContext should take, or have the ability to take a [clonable] context and produce an owned value?