Make sure that the length of the model is serialized too.

src/mlpack/bindings/julia/print_param_defn.hpp

@@ -79,12 +79,14 @@ void PrintParamDefn(
   //   buffer = ccall((:Serialize<Type>Ptr, <programName>Library),
   //       Vector{UInt8}, (Ptr{Nothing}, Ptr{UInt8}), model.ptr,
   //       Base.pointer(buf_len))
-  //   buf = Base.unsafe_wrap(buf_ptr, buf_len[0]; own=true)
+  //   buf = Base.unsafe_wrap(buf_ptr, buf_len[1]; own=true)
+  //   write(stream, buf_len[1])
   //   write(stream, buf)
   // end
   //
   // function deserialize<Type>(stream::IO)::<Type>
-  //   buffer = read(stream)
+  //   buf_len = read(stream, UInt)
+  //   buffer = read(stream, buf_len)
   //   <Type>(ccall((:Deserialize<Type>Ptr, <programName>Library),
   //       Ptr{Nothing}, (Vector{UInt8}, UInt), buffer, length(buffer)))
   // end
@@ -138,6 +140,7 @@ void PrintParamDefn(
       << "Base.pointer(buf_len))" << std::endl;
   std::cout << "  buf = Base.unsafe_wrap(Vector{UInt8}, buf_ptr, buf_len[1]; "
       << "own=true)" << std::endl;
+  std::cout << "  write(stream, buf_len[1])" << std::endl;
   std::cout << "  write(stream, buf)" << std::endl;
   std::cout << "end" << std::endl;
 
@@ -145,7 +148,8 @@ void PrintParamDefn(
   std::cout << "# Deserialize a model from the given stream." << std::endl;
   std::cout << "function deserialize" << type << "(stream::IO)::" << type
       << std::endl;
-  std::cout << "  buffer = read(stream)" << std::endl;
+  std::cout << "  buf_len = read(stream, UInt)" << std::endl;
+  std::cout << "  buffer = read(stream, buf_len)" << std::endl;
   std::cout << "  " << type << "(ccall((:Deserialize" << type << "Ptr, "
       << programName << "Library), Ptr{Nothing}, (Ptr{UInt8}, UInt), "
       << "Base.pointer(buffer), length(buffer)))" << std::endl;

src/mlpack/bindings/julia/tests/runtests.jl

@@ -342,6 +342,27 @@ end
                          model_in=newModel)
 end
 
+# Test that we can serialize a model as part of a larger tuple.
+@testset "TestStreamTupleSerialization" begin
+  _, _, _, _, _, _, modelOut, _, _, _, _, _, _, _ =
+      test_julia_binding(4.0, 12, "hello",
+                         build_model=true)
+
+  stream = IOBuffer()
+  serialize(stream, (modelOut, 3, 4, 5))
+
+  newStream = IOBuffer(copy(stream.data))
+  (newModel, a, b, c) = deserialize(newStream)
+
+  _, _, _, _, _, bwOut, _, _, _, _, _, _, _, _ =
+      test_julia_binding(4.0, 12, "hello",
+                         model_in=newModel)
+
+  @test a == 3
+  @test b == 4
+  @test c == 5
+end
+
 @testset "TestFileSerialization" begin
   _, _, _, _, _, _, modelOut, _, _, _, _, _, _, _ =
       test_julia_binding(4.0, 12, "hello",