Unmarshaling Interface Types in a Union about avro

[nrwiersma]

I see no way to make that work on decoding. TLDR; There is not way to set the interface type (iface).

Basically, I would need something in there of the same type to be able to decode it without falling back to reflect Types and Values. If it is nil, or not of the right type, any attempt to set it would cause a seg fault or a type error. As you cannot create a new iface type, as it instantly becomes nil and an untyped nil at that, and there is no way to convert the decoded type to the iface type, I dont see how this would be doable.

This is not the same case in the encode side, as you already have the type, so none of this type conversion stuff applies here.

This means we can only really support efaces, unless you see another way I am not seeing.

[tylerwendell]

I have been trying to step through the code and figure out how to make it work and I cannot see how to make it work either. Thanks for the quick response. Ill close.

[nrwiersma]

I literally spend 3 hours to try get the initial interface type to accept a new pointer, but to no avail.

[tylerwendell]

There isn't a single go avro library that makes it work. A lot of them won't even marshal union types.

[pckhoi]

Sorry but I don't understand why decoder couldn't be made to work. The decoder could treat interface receivers in this way:

1. Inspect the data and figure out the name of the concrete avro type
2. Look up the registered Go type under that name. If not found, fallback to the old implementation
3. Check if the registered Go type fulfill the given interface, if not return an error
4. Check if the receiver is of the registered type, if not return an error
5. Decode the data into the receiver and profit

Unless there's something else I'm not understanding.

[nrwiersma]

Interface types (iface) are not createable in Go, you are only able to covert a concrete into an iface type. In reflect this possible, but using rtypes and unsafe pointers, there is no mechanism to do this.

Getting the concrete is not an issue, but as the interface is nil, there is no way to get the value out again.