Merge pull request #134 from joshuawarner32/any-struct-list

Add initial implementation of AnyStruct and AnyList

c++/src/capnp/any-test.c++

@@ -106,6 +106,80 @@ TEST(Any, AnyPointer) {
   }
 }
 
+TEST(Any, AnyStruct) {
+  MallocMessageBuilder builder;
+  auto root = builder.getRoot<test::TestAnyPointer>();
+
+  initTestMessage(root.getAnyPointerField().initAs<TestAllTypes>());
+  checkTestMessage(root.getAnyPointerField().getAs<TestAllTypes>());
+  checkTestMessage(root.asReader().getAnyPointerField().getAs<TestAllTypes>());
+
+  EXPECT_EQ(48, root.getAnyPointerField().getAs<AnyStruct>().getDataSection().size());
+  EXPECT_EQ(20, root.getAnyPointerField().getAs<AnyStruct>().getPointerSection().size());
+
+  EXPECT_EQ(48, root.getAnyPointerField().asReader().getAs<AnyStruct>().getDataSection().size());
+  EXPECT_EQ(20, root.getAnyPointerField().asReader().getAs<AnyStruct>().getPointerSection().size());
+
+  auto b = toAny(root.getAnyPointerField().getAs<TestAllTypes>());
+  EXPECT_EQ(48, b.getDataSection().size());
+  EXPECT_EQ(20, b.getPointerSection().size());
+
+  auto r = toAny(root.getAnyPointerField().getAs<TestAllTypes>().asReader());
+  EXPECT_EQ(48, r.getDataSection().size());
+  EXPECT_EQ(20, r.getPointerSection().size());
+
+  r = toAny(root.getAnyPointerField().getAs<TestAllTypes>()).asReader();
+  EXPECT_EQ(48, r.getDataSection().size());
+  EXPECT_EQ(20, r.getPointerSection().size());
+
+  {
+    MallocMessageBuilder b2;
+    auto root2 = b2.getRoot<test::TestAnyPointer>();
+    auto sb = root2.getAnyPointerField().initAsAnyStruct(r.getDataSection().size() / 8, r.getPointerSection().size());
+
+    EXPECT_EQ(48, sb.getDataSection().size());
+    EXPECT_EQ(20, sb.getPointerSection().size());
+
+    // TODO: is there a higher-level API for this?
+    memcpy(sb.getDataSection().begin(), r.getDataSection().begin(), r.getDataSection().size());
+  }
+}
+
+TEST(Any, AnyList) {
+  MallocMessageBuilder builder;
+  auto root = builder.getRoot<test::TestAnyPointer>();
+  List<TestAllTypes>::Builder b = root.getAnyPointerField().initAs<List<TestAllTypes>>(2);
+  initTestMessage(b[0]);
+
+  auto ptr = root.getAnyPointerField().getAs<AnyList>();
+
+  EXPECT_EQ(2, ptr.size());
+  EXPECT_EQ(48, ptr.as<List<AnyStruct>>()[0].getDataSection().size());
+  EXPECT_EQ(20, ptr.as<List<AnyStruct>>()[0].getPointerSection().size());
+
+  auto readPtr = root.getAnyPointerField().asReader().getAs<AnyList>();
+
+  EXPECT_EQ(2, readPtr.size());
+  EXPECT_EQ(48, readPtr.as<List<AnyStruct>>()[0].getDataSection().size());
+  EXPECT_EQ(20, readPtr.as<List<AnyStruct>>()[0].getPointerSection().size());
+
+  auto alb = toAny(root.getAnyPointerField().getAs<List<TestAllTypes>>());
+  EXPECT_EQ(2, alb.size());
+  EXPECT_EQ(48, alb.as<List<AnyStruct>>()[0].getDataSection().size());
+  EXPECT_EQ(20, alb.as<List<AnyStruct>>()[0].getPointerSection().size());
+
+  auto alr = toAny(root.getAnyPointerField().getAs<List<TestAllTypes>>().asReader());
+  EXPECT_EQ(2, alr.size());
+  EXPECT_EQ(48, alr.as<List<AnyStruct>>()[0].getDataSection().size());
+  EXPECT_EQ(20, alr.as<List<AnyStruct>>()[0].getPointerSection().size());
+
+  alr = toAny(root.getAnyPointerField().getAs<List<TestAllTypes>>()).asReader();
+  EXPECT_EQ(2, alr.size());
+  EXPECT_EQ(48, alr.as<List<AnyStruct>>()[0].getDataSection().size());
+  EXPECT_EQ(20, alr.as<List<AnyStruct>>()[0].getPointerSection().size());
+
+}
+
 }  // namespace
 }  // namespace _ (private)
 }  // namespace capnp

c++/src/capnp/any.h

@@ -25,6 +25,7 @@
 #include "layout.h"
 #include "pointer-helpers.h"
 #include "orphan.h"
+#include "list.h"
 
 namespace capnp {
 
@@ -35,6 +36,36 @@ class Orphanage;
 class ClientHook;
 class PipelineHook;
 struct PipelineOp;
+struct AnyPointer;
+
+struct AnyList {
+  AnyList() = delete;
+
+  class Reader;
+  class Builder;
+};
+
+struct AnyStruct {
+  AnyStruct() = delete;
+
+  class Reader;
+  class Builder;
+  class Pipeline;
+};
+
+template<>
+struct List<AnyStruct, Kind::OTHER> {
+  List() = delete;
+
+  class Reader;
+  class Builder;
+};
+
+namespace _ {  // private
+template <> struct Kind_<AnyPointer> { static constexpr Kind kind = Kind::OTHER; };
+template <> struct Kind_<AnyStruct> { static constexpr Kind kind = Kind::OTHER; };
+template <> struct Kind_<AnyList> { static constexpr Kind kind = Kind::OTHER; };
+}  // namespace _ (private)
 
 // =======================================================================================
 // AnyPointer!
@@ -43,6 +74,8 @@ struct AnyPointer {
   // Reader/Builder for the `AnyPointer` field type, i.e. a pointer that can point to an arbitrary
   // object.
 
+  AnyPointer() = delete;
+
   class Reader {
   public:
     typedef AnyPointer Reads;
@@ -54,6 +87,12 @@ struct AnyPointer {
     // Get the total size of the target object and all its children.
 
     inline bool isNull() const;
+    inline bool isStruct() {
+      return reader.isStruct();
+    }
+    inline bool isList() {
+      return reader.isList();
+    }
 
     template <typename T>
     inline ReaderFor<T> getAs() const;
@@ -96,6 +135,12 @@ struct AnyPointer {
     // Get the total size of the target object and all its children.
 
     inline bool isNull();
+    inline bool isStruct() {
+      return builder.isStruct();
+    }
+    inline bool isList() {
+      return builder.isList();
+    }
 
     inline void clear();
     // Set to null.
@@ -132,6 +177,13 @@ struct AnyPointer {
     inline BuilderFor<T> initAs(ListSchema schema, uint elementCount);
     // Only valid for T = DynamicList.  Requires `#include <capnp/dynamic.h>`.
 
+    inline AnyList::Builder initAsAnyList(_::FieldSize elementSize, uint elementCount);
+    // Note: Does not accept INLINE_COMPOSITE for elementSize.
+
+    inline List<AnyStruct>::Builder initAsListOfAnyStruct(uint dataWordCount, uint pointerCount, uint elementCount);
+
+    inline AnyStruct::Builder initAsAnyStruct(uint dataWordCount, uint pointerCount);
+
     template <typename T>
     inline void setAs(ReaderFor<T> value);
     // Valid for ReaderType = T::Reader for T = any generated struct type, List<U>, Text, Data,
@@ -193,11 +245,9 @@ struct AnyPointer {
     // Just make a copy.
 
     Pipeline getPointerField(uint16_t pointerIndex);
-    // Return a new Promise representing a sub-object of the result.  `pointerIndex` is the index
-    // of the sub-object within the pointer section of the result (the result must be a struct).
-    //
-    // TODO(kenton):  On GCC 4.8 / Clang 3.3, use rvalue qualifiers to avoid the need for copies.
-    //   Also make `ops` into a Vector to optimize this.
+    // Deprecated. In the future, we should use .asAnyStruct.getPointerField.
+
+    inline AnyStruct::Pipeline asAnyStruct();
 
     kj::Own<ClientHook> asCap();
     // Expect that the result is a capability and construct a pipelined version of it now.
@@ -282,6 +332,282 @@ private:
   friend class AnyPointer::Builder;
 };
 
+struct AnyList;
+struct AnyStruct;
+
+template <Kind k> struct AnyTypeFor_;
+template <> struct AnyTypeFor_<Kind::STRUCT> { typedef AnyStruct Type; };
+template <> struct AnyTypeFor_<Kind::LIST> { typedef AnyList Type; };
+
+template <typename T>
+using AnyTypeFor = typename AnyTypeFor_<kind<T>()>::Type;
+
+template <typename T>
+inline ReaderFor<AnyTypeFor<FromReader<T>>> toAny(T&& value) {
+  return ReaderFor<AnyTypeFor<FromReader<T> > >(
+      _::PointerHelpers<FromReader<T>>::getInternalReader(value));
+}
+template <typename T>
+inline BuilderFor<AnyTypeFor<FromBuilder<T>>> toAny(T&& value) {
+  return BuilderFor<AnyTypeFor<FromBuilder<T> > >(
+      _::PointerHelpers<FromBuilder<T>>::getInternalBuilder(kj::mv(value)));
+}
+
+template <>
+struct List<AnyPointer, Kind::OTHER> {
+  List() = delete;
+
+  class Reader {
+  public:
+    typedef List<AnyPointer> Reads;
+
+    Reader() = default;
+    inline explicit Reader(_::ListReader reader): reader(reader) {}
+
+    inline uint size() const { return reader.size() / ELEMENTS; }
+    inline typename AnyPointer::Reader operator[](uint index) const {
+      KJ_IREQUIRE(index < size());
+      return typename AnyPointer::Reader(reader.getPointerElement(index * ELEMENTS));
+    }
+
+    typedef _::IndexingIterator<const Reader, typename AnyPointer::Reader> Iterator;
+    inline Iterator begin() const { return Iterator(this, 0); }
+    inline Iterator end() const { return Iterator(this, size()); }
+
+  private:
+    _::ListReader reader;
+    template <typename U, Kind K>
+    friend struct _::PointerHelpers;
+    template <typename U, Kind K>
+    friend struct List;
+    friend class Orphanage;
+    template <typename U, Kind K>
+    friend struct ToDynamic_;
+  };
+
+  class Builder {
+  public:
+    typedef List<AnyPointer> Builds;
+
+    Builder() = delete;
+    inline Builder(decltype(nullptr)) {}
+    inline explicit Builder(_::ListBuilder builder): builder(builder) {}
+
+    inline operator Reader() { return Reader(builder.asReader()); }
+    inline Reader asReader() { return Reader(builder.asReader()); }
+
+    inline uint size() const { return builder.size() / ELEMENTS; }
+    inline typename AnyPointer::Builder operator[](uint index) {
+      KJ_IREQUIRE(index < size());
+      return typename AnyPointer::Builder(builder.getPointerElement(index * ELEMENTS));
+    }
+
+    typedef _::IndexingIterator<Builder, typename AnyPointer::Builder> Iterator;
+    inline Iterator begin() { return Iterator(this, 0); }
+    inline Iterator end() { return Iterator(this, size()); }
+
+  private:
+    _::ListBuilder builder;
+    template <typename U, Kind K>
+    friend struct _::PointerHelpers;
+    friend class Orphanage;
+    template <typename U, Kind K>
+    friend struct ToDynamic_;
+  };
+};
+
+class AnyStruct::Reader {
+public:
+  Reader() = default;
+  inline Reader(_::StructReader reader): _reader(reader) {}
+
+  Data::Reader getDataSection() {
+    return _reader.getDataSectionAsBlob();
+  }
+  List<AnyPointer>::Reader getPointerSection() {
+    return List<AnyPointer>::Reader(_reader.getPointerSectionAsList());
+  }
+
+  template <typename T>
+  ReaderFor<T> as();
+  // T must be a struct type.
+private:
+  _::StructReader _reader;
+};
+
+class AnyStruct::Builder {
+public:
+  inline Builder(decltype(nullptr)) {}
+  inline Builder(_::PointerBuilder builder, _::StructSize size, const word* defaultValue = nullptr): _builder(builder.getStruct(size, defaultValue)) {}
+  inline Builder(_::StructBuilder builder): _builder(builder) {}
+
+  inline Data::Builder getDataSection() {
+    return _builder.getDataSectionAsBlob();
+  }
+  List<AnyPointer>::Builder getPointerSection() {
+    return List<AnyPointer>::Builder(_builder.getPointerSectionAsList());
+  }
+
+  inline operator Reader() const { return Reader(_builder.asReader()); }
+  inline Reader asReader() const { return Reader(_builder.asReader()); }
+private:
+  _::StructBuilder _builder;
+  friend class Orphanage;
+  friend class CapBuilderContext;
+};
+
+class AnyStruct::Pipeline {
+public:
+  Pipeline getPointerField(uint16_t pointerIndex);
+  // Return a new Promise representing a sub-object of the result.  `pointerIndex` is the index
+  // of the sub-object within the pointer section of the result (the result must be a struct).
+  //
+  // TODO(kenton):  On GCC 4.8 / Clang 3.3, use rvalue qualifiers to avoid the need for copies.
+  //   Also make `ops` into a Vector to optimize this.
+
+private:
+  kj::Own<PipelineHook> hook;
+  kj::Array<PipelineOp> ops;
+
+  inline Pipeline(kj::Own<PipelineHook>&& hook, kj::Array<PipelineOp>&& ops)
+      : hook(kj::mv(hook)), ops(kj::mv(ops)) {}
+
+};
+
+class List<AnyStruct, Kind::OTHER>::Reader {
+public:
+  typedef List<AnyStruct> Reads;
+
+  Reader() = default;
+  inline explicit Reader(_::ListReader reader): reader(reader) {}
+
+  inline uint size() const { return reader.size() / ELEMENTS; }
+  inline typename AnyStruct::Reader operator[](uint index) const {
+    KJ_IREQUIRE(index < size());
+    return typename AnyStruct::Reader(reader.getStructElement(index * ELEMENTS));
+  }
+
+  typedef _::IndexingIterator<const Reader, typename AnyStruct::Reader> Iterator;
+  inline Iterator begin() const { return Iterator(this, 0); }
+  inline Iterator end() const { return Iterator(this, size()); }
+
+private:
+  _::ListReader reader;
+  template <typename U, Kind K>
+  friend struct _::PointerHelpers;
+  template <typename U, Kind K>
+  friend struct List;
+  friend class Orphanage;
+  template <typename U, Kind K>
+  friend struct ToDynamic_;
+};
+
+
+class List<AnyStruct, Kind::OTHER>::Builder {
+public:
+  typedef List<AnyStruct> Builds;
+
+  Builder() = delete;
+  inline Builder(decltype(nullptr)) {}
+  inline explicit Builder(_::ListBuilder builder): builder(builder) {}
+
+  inline operator Reader() { return Reader(builder.asReader()); }
+  inline Reader asReader() { return Reader(builder.asReader()); }
+
+  inline uint size() const { return builder.size() / ELEMENTS; }
+  inline typename AnyStruct::Builder operator[](uint index) {
+    KJ_IREQUIRE(index < size());
+    return typename AnyStruct::Builder(builder.getStructElement(index * ELEMENTS));
+  }
+
+  typedef _::IndexingIterator<Builder, typename AnyStruct::Builder> Iterator;
+  inline Iterator begin() { return Iterator(this, 0); }
+  inline Iterator end() { return Iterator(this, size()); }
+
+private:
+  _::ListBuilder builder;
+  template <typename U, Kind K>
+  friend struct _::PointerHelpers;
+  friend class Orphanage;
+  template <typename U, Kind K>
+  friend struct ToDynamic_;
+};
+
+class AnyList::Reader {
+public:
+  Reader() = default;
+  inline Reader(_::ListReader reader): _reader(reader) {}
+
+  _::FieldSize getElementSize();
+  ElementCount size() {
+    return _reader.size();
+  }
+
+  template <typename T> ReaderFor<T> as() {
+  // T must be List<U>.
+    return ReaderFor<T>(_reader);
+  }
+private:
+  _::ListReader _reader;
+};
+
+class AnyList::Builder {
+public:
+  inline Builder(decltype(nullptr)) {}
+  inline Builder(_::PointerBuilder builder, _::FieldSize size, const word* defaultValue = nullptr): _builder(builder.getList(size, defaultValue)) {}
+  inline Builder(_::ListBuilder builder): _builder(builder) {}
+
+  _::FieldSize getElementSize();
+  ElementCount size() {
+    return _builder.size();
+  }
+
+  template <typename T> BuilderFor<T> as() {
+  // T must be List<U>.
+    return BuilderFor<T>(_builder);
+  }
+
+  inline operator Reader() const { return Reader(_builder.asReader()); }
+  inline Reader asReader() const { return Reader(_builder.asReader()); }
+
+private:
+  _::ListBuilder _builder;
+};
+
+namespace _ { // (private)
+template <>
+struct PointerHelpers<AnyStruct, Kind::OTHER> {
+  static inline typename AnyStruct::Reader get(PointerReader reader, const word* defaultValue = nullptr) {
+    return typename AnyStruct::Reader(reader.getStruct(defaultValue));
+  }
+  static inline typename AnyStruct::Builder get(PointerBuilder builder,
+                                        const word* defaultValue = nullptr) {
+    return typename AnyStruct::Builder(builder, /* TODO: allow specifying the size! */ _::StructSize(0, 0), defaultValue);
+  }
+  static inline typename AnyStruct::Builder init(PointerBuilder builder, uint dataWordCount, uint pointerCount) {
+    return typename AnyStruct::Builder(builder.initStruct(StructSize(dataWordCount, pointerCount)));
+  }
+};
+template <>
+struct PointerHelpers<AnyList, Kind::OTHER> {
+  static inline typename AnyList::Reader get(PointerReader reader, const word* defaultValue = nullptr) {
+    return typename AnyList::Reader(reader.getList(/* TODO: allow specifying the size! */ FieldSize::VOID, defaultValue));
+  }
+  static inline typename AnyList::Builder get(PointerBuilder builder,
+                                        const word* defaultValue = nullptr) {
+    return typename AnyList::Builder(builder, /* TODO: allow specifying the size! */ FieldSize::VOID, defaultValue);
+  }
+  static inline typename AnyList::Builder init(PointerBuilder builder, FieldSize elementSize, uint elementCount) {
+    return typename AnyList::Builder(builder.initList(elementSize, elementCount));
+  }
+  static inline typename AnyList::Builder init(PointerBuilder builder, uint dataWordCount, uint pointerCount, uint elementCount) {
+    return typename AnyList::Builder(builder.initStructList(
+        elementCount,
+        StructSize(dataWordCount, pointerCount)));
+  }
+};
+} // end namespace _ (private)
+
 // =======================================================================================
 // Pipeline helpers
 //
@@ -331,10 +657,6 @@ public:
 // =======================================================================================
 // Inline implementation details
 
-namespace _ {  // private
-template <> struct Kind_<AnyPointer> { static constexpr Kind kind = Kind::OTHER; };
-}  // namespace _ (private)
-
 inline MessageSize AnyPointer::Reader::targetSize() const {
   return reader.targetSize().asPublic();
 }
@@ -375,6 +697,16 @@ inline BuilderFor<T> AnyPointer::Builder::initAs(uint elementCount) {
   return _::PointerHelpers<T>::init(builder, elementCount);
 }
 
+inline AnyList::Builder AnyPointer::Builder::initAsAnyList(_::FieldSize elementSize, uint elementCount) {
+  return _::PointerHelpers<AnyList>::init(builder, elementSize, elementCount);
+}
+
+// inline List<AnyStruct>::Builder AnyPointer::Builder::initAsListOfAnyStruct(uint dataWordCount, uint pointerCount, uint elementCount);
+
+inline AnyStruct::Builder AnyPointer::Builder::initAsAnyStruct(uint dataWordCount, uint pointerCount) {
+  return _::PointerHelpers<AnyStruct>::init(builder, dataWordCount, pointerCount);
+}
+
 template <typename T>
 inline void AnyPointer::Builder::setAs(ReaderFor<T> value) {
   return _::PointerHelpers<T>::set(builder, value);
@@ -402,6 +734,8 @@ inline Orphan<AnyPointer> AnyPointer::Builder::disown() {
 
 template <> struct ReaderFor_ <AnyPointer, Kind::OTHER> { typedef AnyPointer::Reader Type; };
 template <> struct BuilderFor_<AnyPointer, Kind::OTHER> { typedef AnyPointer::Builder Type; };
+template <> struct ReaderFor_ <AnyStruct, Kind::OTHER> { typedef AnyStruct::Reader Type; };
+template <> struct BuilderFor_<AnyStruct, Kind::OTHER> { typedef AnyStruct::Builder Type; };
 
 template <>
 struct Orphanage::GetInnerReader<AnyPointer, Kind::OTHER> {

c++/src/capnp/compiler/capnpc-c++.c++

@@ -1700,6 +1700,8 @@ private:
         "  template <typename, ::capnp::Kind>\n"
         "  friend struct ::capnp::ToDynamic_;\n"
         "  friend class ::capnp::Orphanage;\n",
+        "  template <typename, ::capnp::Kind>\n"
+        "  friend struct ::capnp::_::PointerHelpers;\n"
         "};\n"
         "\n");
   }

c++/src/capnp/layout.c++

@@ -251,6 +251,7 @@ struct WirePointer {
     // our "null" value.
     return (offsetAndKind.get() == 0) & (upper32Bits == 0);
   }
+
 };
 static_assert(sizeof(WirePointer) == sizeof(word),
     "capnp::WirePointer is not exactly one word.  This will probably break everything.");
@@ -2155,6 +2156,20 @@ bool PointerBuilder::isNull() {
   return pointer->isNull();
 }
 
+bool PointerBuilder::isStruct() {
+  word* refTarget;
+  WirePointer* ptr = pointer;
+  WireHelpers::followFars(ptr, refTarget, segment);
+  return ptr->kind() == WirePointer::Kind::STRUCT;
+}
+
+bool PointerBuilder::isList() {
+  word* refTarget;
+  WirePointer* ptr = pointer;
+  WireHelpers::followFars(ptr, refTarget, segment);
+  return ptr->kind() == WirePointer::Kind::LIST;
+}
+
 void PointerBuilder::transferFrom(PointerBuilder other) {
   if (!pointer->isNull()) {
     WireHelpers::zeroObject(segment, pointer);
@@ -2238,6 +2253,22 @@ bool PointerReader::isNull() const {
   return pointer == nullptr || pointer->isNull();
 }
 
+bool PointerReader::isStruct() const {
+  word* refTarget;
+  const WirePointer* ptr = pointer;
+  SegmentReader* sgmt = segment;
+  WireHelpers::followFars(ptr, refTarget, sgmt);
+  return ptr->kind() == WirePointer::Kind::STRUCT;
+}
+
+bool PointerReader::isList() const {
+  word* refTarget;
+  const WirePointer* ptr = pointer;
+  SegmentReader* sgmt = segment;
+  WireHelpers::followFars(ptr, refTarget, sgmt);
+  return ptr->kind() == WirePointer::Kind::LIST;
+}
+
 kj::Maybe<Arena&> PointerReader::getArena() const {
   return segment == nullptr ? nullptr : segment->getArena();
 }

c++/src/capnp/layout.h

@@ -324,6 +324,8 @@ public:
   // location.
 
   bool isNull();
+  bool isStruct();
+  bool isList();
 
   StructBuilder getStruct(StructSize size, const word* defaultValue);
   ListBuilder getList(FieldSize elementSize, const word* defaultValue);
@@ -402,6 +404,8 @@ public:
   // exception if it overruns.
 
   bool isNull() const;
+  bool isStruct() const;
+  bool isList() const;
 
   StructReader getStruct(const word* defaultValue) const;
   ListReader getList(FieldSize expectedElementSize, const word* defaultValue) const;
@@ -452,6 +456,7 @@ public:
   inline BitCount getDataSectionSize() const { return dataSize; }
   inline WirePointerCount getPointerSectionSize() const { return pointerCount; }
   inline Data::Builder getDataSectionAsBlob();
+  inline _::ListBuilder getPointerSectionAsList();
 
   template <typename T>
   KJ_ALWAYS_INLINE(bool hasDataField(ElementCount offset));
@@ -532,6 +537,7 @@ public:
   inline BitCount getDataSectionSize() const { return dataSize; }
   inline WirePointerCount getPointerSectionSize() const { return pointerCount; }
   inline Data::Reader getDataSectionAsBlob();
+  inline _::ListReader getPointerSectionAsList();
 
   template <typename T>
   KJ_ALWAYS_INLINE(bool hasDataField(ElementCount offset) const);
@@ -662,6 +668,7 @@ private:
   friend class StructBuilder;
   friend struct WireHelpers;
   friend class OrphanBuilder;
+  friend class AnyStruct;
 };
 
 class ListReader {
@@ -846,6 +853,10 @@ inline Data::Builder StructBuilder::getDataSectionAsBlob() {
   return Data::Builder(reinterpret_cast<byte*>(data), dataSize / BITS_PER_BYTE / BYTES);
 }
 
+inline _::ListBuilder StructBuilder::getPointerSectionAsList() {
+  return _::ListBuilder(segment, pointers, pointerCount * BITS_PER_WORD / ELEMENTS, pointerCount, 0, 1, FieldSize::POINTER);
+}
+
 template <typename T>
 inline bool StructBuilder::hasDataField(ElementCount offset) {
   return getDataField<Mask<T>>(offset) != 0;
@@ -924,6 +935,10 @@ inline Data::Reader StructReader::getDataSectionAsBlob() {
   return Data::Reader(reinterpret_cast<const byte*>(data), dataSize / BITS_PER_BYTE / BYTES);
 }
 
+inline _::ListReader StructReader::getPointerSectionAsList() {
+  return _::ListReader(segment, pointers, pointerCount, pointerCount * BITS_PER_WORD / ELEMENTS, 0, 1, FieldSize::POINTER, nestingLimit);
+}
+
 template <typename T>
 inline bool StructReader::hasDataField(ElementCount offset) const {
   return getDataField<Mask<T>>(offset) != 0;

c++/src/capnp/list.h

@@ -163,6 +163,8 @@ struct List<T, Kind::PRIMITIVE> {
 
   private:
     _::ListBuilder builder;
+    template <typename U, Kind K>
+    friend struct _::PointerHelpers;
     friend class Orphanage;
     template <typename U, Kind K>
     friend struct ToDynamic_;
@@ -282,6 +284,8 @@ struct List<T, Kind::STRUCT> {
 
   private:
     _::ListBuilder builder;
+    template <typename U, Kind K>
+    friend struct _::PointerHelpers;
     friend class Orphanage;
     template <typename U, Kind K>
     friend struct ToDynamic_;
@@ -391,6 +395,8 @@ struct List<List<T>, Kind::LIST> {
 
   private:
     _::ListBuilder builder;
+    template <typename U, Kind K>
+    friend struct _::PointerHelpers;
     friend class Orphanage;
     template <typename U, Kind K>
     friend struct ToDynamic_;
@@ -487,6 +493,8 @@ struct List<T, Kind::BLOB> {
 
   private:
     _::ListBuilder builder;
+    template <typename U, Kind K>
+    friend struct _::PointerHelpers;
     friend class Orphanage;
     template <typename U, Kind K>
     friend struct ToDynamic_;

c++/src/capnp/pointer-helpers.h

@@ -24,6 +24,7 @@
 
 #include "layout.h"
 #include "list.h"
+// #include "any.h"
 
 namespace capnp {
 namespace _ {  // private
@@ -53,13 +54,12 @@ struct PointerHelpers<T, Kind::STRUCT> {
   static inline Orphan<T> disown(PointerBuilder builder) {
     return Orphan<T>(builder.disown());
   }
-
   static inline _::StructReader getInternalReader(const typename T::Reader& reader) {
-    // TODO(cleanup):  This is used by RpcSystem::Connect, but perhaps it should be used more
-    //   broadly so that we can reduce the number of friends declared by every Reader type.
-
     return reader._reader;
   }
+  static inline _::StructBuilder getInternalBuilder(typename T::Builder&& builder) {
+    return builder._builder;
+  }
 };
 
 template <typename T>
@@ -91,6 +91,12 @@ struct PointerHelpers<List<T>, Kind::LIST> {
   static inline Orphan<List<T>> disown(PointerBuilder builder) {
     return Orphan<List<T>>(builder.disown());
   }
+  static inline _::ListReader getInternalReader(const typename List<T>::Reader& reader) {
+    return reader.reader;
+  }
+  static inline _::ListBuilder getInternalBuilder(typename List<T>::Builder&& builder) {
+    return builder.builder;
+  }
 };
 
 template <typename T>