I am writing an application that reads incoming packets and I’d like to decode them and route them to the appropriate handler. The header of each packet is what defines its type. So for example a user login packet may look like this: << header::integer-little-8, ulen::unsigned-little-integer-…

[image] Ripster: I’ve been messing around with require quite a bit and still can’t seem to get it to work. What seems to be happening is Mix.Tasks.Xref.calls() comes up empty on first compile. If I edit what seems to be just about any file related to the router and then recompile, it comes up wi…

My current favorite library to read for learning about neat code generation is NimbleParsec . It might give you some ideas. :slight_smile: Edit: The Elixir Forum thread for the library is also good- searching it for “quoted expressions” might give you a few more ideas.

I don’t think you need a macro for this. Something like this should do it. Of course you would probably encapsulate the header->function mapping differently in real use rather than a module attribute. defmodule Dynamic do @function_map [ {1, Packets.Login}, {2, Packets.Chat} ] def…

Part of my goal is to avoid creating a map of header => Module manually. I want the packet header to be part of the packet definition and all the parse functions to be generated. I just can’t seem to figure out how to create that list at compile time. Heck if I could even just extend the Packet mod…

[image] Ripster: I just can’t seem to figure out how to create that list at compile time. Um, so how do you know at compile type what the packet types are, and what the processing should be for each packet? I’m surely misunderstanding you but it sounds like you’re saying something like this,…

You’re right that I want to pattern match on the header. I want the header to be defined in the module that handles the actual packet though. Otherwise you end up with a module that is nothing but a large list mapping the header numbers to modules. I don’t want to separate that information. If I wa…

Here’s some code that will introspect the known modules and identify if they implement a behaviour. I’ve shown two ways to get the known modules, one is Elixir release dependent, the other uses the Mix api. Both are really only available in a build environment but I guess thats OK for your use. The…

Using the code above you could then generate the functions you’re after with something like: defmodule PacketHandler do @moduledoc """ Assuming the @behaviour :packet includes the callback `:packet_type` to return the type of packet it processes """ for module <- Implementation.behaviou…

[image] Ripster: If I was able to get every module that has use Packet, header: 1 or implements a Packet behaviour, or every module with a @packet_header attribute, then I could build the list without having to list them all out manually. I really should release my library of mine that does …

For some reason the functions are not getting generated unless I compile the app, modify the router I have defined 2 modules packet.ex defmodule Packet do @callback packet_type() :: integer @callback parse(any) :: {:ok, struct} @callback run(struct) :: :ok | {:ok, any} | {:error, String.t()…

[image] Ripster: If I compile the app and then modify server/packet/router.ex (add or remove a blank line) then recompile the parse function does get generated. That just means the compile cannot figure out the dependency chain properly, adding some require’s would help that but that would mi…

Function generation / dynamic dispatch

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OvermindDL1 March 30, 2018, 9:50pm 15

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