1 // Protocol Buffers - Google's data interchange format 2 // Copyright 2024 Google LLC. All rights reserved. 3 // 4 // Use of this source code is governed by a BSD-style 5 // license that can be found in the LICENSE file or at 6 // https://developers.google.com/open-source/licenses/bsd 7 8 use super::upb_MiniTable; 9 10 /// A trait for types which have a constant associated MiniTable (e.g. 11 /// generated messages, and their mut and view proxy types). 12 /// 13 /// upb_Message in C is effectively a DST type, where instances are created with 14 /// a MiniTable (and have a size dependent on the given MiniTable). Many upb 15 /// operations on the upb_Message* will require the same upb_MiniTable* to be 16 /// passed in as a parameter, which is referred to as 'the associated MiniTable 17 /// for the upb_Message instance' in safety comments. 18 /// 19 /// This trait is a way to associate a MiniTable with Rust types 20 /// which hold upb_Message* to simplify ensuring the upb C invariants 21 /// are maintained. 22 /// 23 /// Note that this would prefer to be a `const MINI_TABLE: *const upb_MiniTable` 24 /// to statically associate a single MiniTable, but as long as the MiniTable is 25 /// an extern "C" we cannot do that without the unstable `const_refs_to_static`. 26 /// After that feature is stabilized (or if we move the MiniTable generation to 27 /// .rs) this will be switched. 28 /// 29 /// SAFETY: 30 /// - The MiniTable pointer must be from Protobuf code generation and follow the 31 /// corresponding invariants associated with upb's C API (the pointer should 32 /// always have the same non-null value, the underlying pointee should never 33 /// be modified and should have 'static lifetime). 34 pub unsafe trait AssociatedMiniTable { mini_table() -> *const upb_MiniTable35 fn mini_table() -> *const upb_MiniTable; 36 } 37