Rake task arguments are not hashes.

Published on Apr 10, 2014

I was creating a rake task today that take some arguments from the command line and I wanted to use those arguments to create an object.

I needed to merge the given arguments with some generated values inside the task so the code originally looked something like this.

    task :create, [:first_name, :last_name, :email] => :environment do |t, args|
        args.merge!({seed: generate_password})
        user = User.create(args)
        p user

After running the task the User was created with no information at all!

After verifying that args had the proper values I did a quick test and noticed that merge! on args didn't work, printing args it looked like a hash but inspecting the type I noticed that is not a simple hash but a "Rake::TaskArguments":http://rake.rubyforge.org/classes/Rake/TaskArguments.html and there is not merge method.

I have been using task arguments for some time now but I guess I never had to do this before. I would expect calling merge to raise an exception and not fail silently.

I didn't look into the implementation of the class (the actual code) but in the documentation it looks like method_missing will delegate to a protected look_up method that will check for the existence of a key in the internal hash, ENV or parent object and silently fail otherwise.

The fix is simple, since Rake::TaskArguments has a to_hash method. The revisited code looks like this.

    task :create, [:first_name, :last_name, :email] => :environment do |t, args|
        opts = args.to_hash.merge({seed: generate_password})
        user = User.create(opts)
        p user

I hope this can save somebody a few minutes of their time.