Pros of OTP

• Comprehensive standard library and runtime system for building scalable, fault-tolerant applications
• Includes built-in support for concurrency, distribution, and hot code reloading
• Provides a complete ecosystem for developing and deploying Erlang applications

Cons of OTP

• Steeper learning curve due to its extensive features and concepts
• Larger codebase and more complex structure compared to Rebar3
• May be overkill for smaller projects or those not requiring all OTP features

Code Comparison

OTP (supervisor behavior):

init([]) ->
    {ok, {{one_for_one, 5, 10},
          [{my_server, {my_server, start_link, []},
            permanent, 5000, worker, [my_server]}]}}.

Rebar3 (rebar.config):

{erl_opts, [debug_info]}.
{deps, []}.
{plugins, [rebar3_auto]}.
{shell, [{apps, [my_app]}]}.

Summary

OTP is a comprehensive framework for building robust Erlang applications, offering a wide range of features and tools. Rebar3, on the other hand, is a build tool and package manager for Erlang projects. While OTP provides the core runtime and libraries, Rebar3 simplifies project management and dependency handling. OTP is better suited for large-scale, distributed systems, while Rebar3 excels in streamlining the development workflow for Erlang projects of various sizes.

Pros of Elixir

• Built-in support for metaprogramming and macros, enabling more expressive and concise code
• Improved syntax and modern language features, making it more approachable for developers coming from other languages
• Integrated tooling, including mix for project management, testing, and dependency handling

Cons of Elixir

• Smaller ecosystem compared to Erlang, with fewer libraries and resources available
• Potential performance overhead due to additional language abstractions
• Learning curve for developers unfamiliar with functional programming concepts

Code Comparison

Elixir:

defmodule Hello do
  def world do
    IO.puts "Hello, World!"
  end
end

Erlang (using rebar3):

-module(hello).
-export([world/0]).

world() ->
    io:format("Hello, World!~n").

Both examples achieve the same result, but Elixir's syntax is more concise and resembles modern programming languages. Erlang's syntax is more traditional and may be less intuitive for developers coming from other language backgrounds.

While rebar3 is a build tool for Erlang projects, Elixir comes with mix, which provides similar functionality out of the box. This integrated approach in Elixir can lead to a more streamlined development experience, especially for newcomers to the BEAM ecosystem.

Pros of Cowboy

• Specialized HTTP server library for Erlang/OTP, offering high performance and low latency
• Supports both HTTP/1.1 and HTTP/2, as well as WebSockets
• Lightweight and modular design, allowing for easy customization

Cons of Cowboy

• Narrower scope compared to Rebar3, focusing solely on HTTP server functionality
• Steeper learning curve for developers new to Erlang or HTTP server implementation
• May require additional tools or libraries for a complete web application stack

Code Comparison

Cowboy (HTTP server setup):

start(_Type, _Args) ->
    Dispatch = cowboy_router:compile([
        {'_', [{"/", my_handler, []}]}
    ]),
    {ok, _} = cowboy:start_clear(my_http_listener,
        [{port, 8080}],
        #{env => #{dispatch => Dispatch}}
    ),
    my_app_sup:start_link().

Rebar3 (Project configuration):

{erl_opts, [debug_info]}.
{deps, [
    {cowboy, "2.9.0"}
]}.
{relx, [{release, {my_app, "0.1.0"},
         [my_app, sasl]},
        {mode, dev}]}.

Note: The code snippets demonstrate different aspects of each project, as Rebar3 is a build tool and Cowboy is an HTTP server library.

Pros of EMQX

• Specialized MQTT broker with extensive IoT messaging features
• Scalable architecture supporting millions of concurrent connections
• Rich plugin ecosystem for extending functionality

Cons of EMQX

• More complex setup and configuration compared to Rebar3
• Narrower focus on MQTT and IoT, less versatile for general Erlang projects
• Steeper learning curve for developers new to MQTT or IoT

Code Comparison

EMQX configuration example:

{emqx, [
  {listeners, [
    {tcp, 1883, [{acceptors, 16}, {max_connections, 512000}]}
  ]},
  {mqtt, [
    {allow_anonymous, true},
    {max_clientid_len, 1024}
  ]}
]}

Rebar3 configuration example:

{erl_opts, [debug_info]}.
{deps, [
  {cowboy, "2.9.0"},
  {jsx, "3.1.0"}
]}.
{relx, [{release, {my_app, "0.1.0"}, [my_app]}]}.

While EMQX focuses on MQTT broker configuration, Rebar3 is a build tool for managing Erlang projects, dependencies, and releases. EMQX provides a more specialized solution for IoT messaging, while Rebar3 offers broader project management capabilities for Erlang development.

Pros of ejabberd

• Specialized XMPP server with extensive messaging features
• Highly scalable and robust for real-time communication applications
• Active community and regular updates for security and performance

Cons of ejabberd

• Steeper learning curve for non-XMPP developers
• More complex setup and configuration compared to general-purpose build tools
• Limited use cases outside of XMPP/messaging applications

Code Comparison

ejabberd (XMPP stanza handling):

handle_info({route, From, To, Packet}, State) ->
    case catch do_route(From, To, Packet) of
        {'EXIT', Reason} ->
            ?ERROR_MSG("error routing packet: ~p", [Reason]);
        _ -> ok
    end,
    {noreply, State}.

rebar3 (Plugin compilation):

compile(State, Apps) ->
    [begin
         Opts = rebar_app_info:opts(AppInfo),
         AppDir = rebar_app_info:dir(AppInfo),
         compile_app(State, Opts, AppDir)
     end || AppInfo <- Apps],
    {ok, State}.

While ejabberd focuses on XMPP protocol handling and messaging functionality, rebar3 is a general-purpose Erlang build tool. ejabberd is better suited for developers building messaging systems, while rebar3 is more versatile for various Erlang projects. The code snippets highlight their different purposes: ejabberd deals with routing XMPP packets, while rebar3 manages compilation of Erlang applications.