Admit arbitrary ProtoType for read and write

src/core.jl

@@ -3,6 +3,7 @@ using Base.Threads
 using CodecZlib
 using BufferedStreams
 using MacroTools: @forward
+using ProtoBuf: ProtoType
 
 # Ref: https://github.com/tensorflow/tensorflow/blob/295ad2781683835be974faba0a191528d8079768/tensorflow/core/lib/hash/crc32c.h#L50-L59
 
@@ -62,10 +63,10 @@ read(f, s::String; kwargs...) = read(f, [s]; kw...)
 function read(
     f,
     files::Vector;
-    compression=nothing,
-    bufsize=10*1024*1024,
-    channel_size=1_000,
-    record_type=Example
+    compression = nothing,
+    bufsize = 10 * 1024 * 1024,
+    channel_size = 1_000,
+    record_type = Example,
 )
     Channel{record_type}(channel_size) do ch
         @threads for file_name in files
@@ -77,12 +78,13 @@ function read(
                 elseif compression == :zlib
                     io = ZlibDecompressorStream(io)
                 else
-                    isnothing(compression) || throw(ArgumentError("unsupported compression method: $compression"))
+                    isnothing(compression) ||
+                        throw(ArgumentError("unsupported compression method: $compression"))
                 end
 
                 while !eof(io)
-                    example = readproto(IOBuffer(read_record(io)), Example())
-                    put!(ch, f(example))
+                    instance = readproto(IOBuffer(read_record(io)), record_type())
+                    put!(ch, f(instance))
                 end
             end
         end
@@ -128,7 +130,7 @@ function write(io::IO, xs)
     end
 end
 
-function write(io::IO, x::Example)
+function write(io::IO, x::ProtoType)
     buff = IOBuffer()
     writeproto(buff, x)