One area that the Go SDK currently lacks: is the ability for users to specify their own coders for types.
I've written a proposal document, <https://docs.google.com/document/d/1kQwx4Ah6PzG8z2ZMuNsNEXkGsLXm6gADOZaIO7reUOg/edit#> and while I'm confident about the core, there are certainly some edge cases that require discussion before getting on with the implementation. At presently, the SDK only permits primitive value types (all numeric types but complex, strings, and []bytes) which are coded with beam coders, and structs whose exported fields are of those type, which is then encoded as JSON. Protocol buffer support is hacked in to avoid the type anaiyzer, and presents the current work around this issue. The high level proposal is to catch up with Python and Java, and have a coder registry. In addition, arrays, and maps should be permitted as well. If you have alternatives, or other suggestions and opinions, I'd love to hear them! Otherwise my intent is to get a PR ready by the end of January. Thanks! Robert Burke
