Go Protobuf: The New Opaque API(go.dev)

    type Info struct {
      User LazyProto[User]
    }

    userName := user.Get().Name

  type LogEntry_builder struct {
   BackendServer *string
   RequestSize   *uint32
   IpAddress     *string
   // contains filtered or unexported fields
  }

  func (b0 LogEntry_builder) Build() *LogEntry

   message M {
      string foo = 1;
   }
   message N {
       M bar = 2;
   }

   type WithID interface { GetId() []byte }

   func Put(tx *Tx, x WithID) error { ... }
   func Get(tx *Tx, id []byte) (WithId, error) { ... } 

  - Messages (especially opaque ones) are not supposed to be copied. The
    recommendation is to use `m := &mypb.Message{}`.
  - This would make migrating to use the opaque API more difficult, if the
    getters don't return the same type as the old open API fields, much more
    code needs to be rewritten, or some wrapper that allocates a new slice on
    every get.
  - Users expect that `subm := m.GetSubMessages()[2] ;
    m.SetSubMessages(append(m.GetSubMessages(), anotherm))) ; subm.SetInt(42) ;
    assert(subm.GetInt() == m.GetSubMessages()[2].GetInt())`. This would not be
    the case if the API returned a slice of values.
  - ...

  - Allocations when passing iterators to functions that expect a slice.
  - Extra API surface for modifying the list (append, getn, len, ...).

  for i := range valuel {
    ptrl[i] = &valuel[i] // TODO: verify that this escape doesn't cause disjoint allocations.
  }