Ruby vs Rails

I always find it interesting when I hit a Rails-ism when I'm working in a pure Ruby context. I define a Rails-ism as something that is one way in Ruby and another way in Rails. In this case I'm writing a simple background daemon which is going to stream data out of the Twitter sample stream and commit to Kafka for downstream processing.

Here's the first thing that bit me:

TOPIC = ENV['TOPIC']

if TOPIC.blank?
  puts "No topic specified; exiting"
  exit
end

And this gave an immediate failure:

❯ TOPIC=twitter RAILS_ENV=development ruby kafka_loader.rb
Traceback (most recent call last):
kafka_loader.rb:19:in `<main>': undefined method `blank?' for "twitter":String (NoMethodError)

The easiest way to understand something like this is to test it in irb. The irb tool is the underlying engine in rails console ("rails c") but without your application specific classes loaded in so it is just pure ruby.

Here's how you would test something like this in irb:

2.7.0 :001 > "".blank?
Traceback (most recent call last):
       16: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/friendly_errors.rb:123:in `with_friendly_errors'
       15: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/gems/2.7.0/gems/bundler-2.1.2/libexec/bundle:46:in `block in <top (required)>'
       14: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli.rb:24:in `start'
       13: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/vendor/thor/lib/thor/base.rb:476:in `start'
       12: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli.rb:30:in `dispatch'
       11: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/vendor/thor/lib/thor.rb:399:in `dispatch'
       10: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
        9: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
        8: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli.rb:476:in `exec'
        7: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli/exec.rb:28:in `run'
        6: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli/exec.rb:63:in `kernel_load'
        5: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli/exec.rb:63:in `load'
        4: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/bin/irb:23:in `<top (required)>'
        3: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/bin/irb:23:in `load'
        2: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/gems/2.7.0/gems/irb-1.2.1/exe/irb:11:in `<top (required)>'
        1: from (irb):1
NoMethodError (undefined method `blank?' for "":String)
2.7.0 :002 > "".empty?
 => true
2.7.0 :003 >

Off the top of my head, I knew that .empty? was the underlying method that .blank? was aliased to. And I could test either of these on an empty string as a way to figure this out. When you have this type of thing, a quick google for "rails whatever" often is all you need to understand it. The top hit for rails blank? was a nicely written piece by Arkency.

Another example of this came up here:

Traceback (most recent call last):
	1: from kafka_loader.rb:188:in `<main>'
kafka_loader.rb:77:in `kafka_connect': undefined method `second' for #<Array:0x00007fe197c3d4c8> (NoMethodError)

In this case, again, I knew that .second was a method that Rails sticks into the array class. The fix here was to move to:

[0]  and [1]

to access the first and second elements in the array.

You can easily see that .first actually works on arrays but I moved to [0] and [1] anyway to keep the semantics of the code the same:

❯ irb
cannot load such file -- awesome_print
2.7.0 :001 > foo = []
2.7.0 :002 > foo.first
 => nil
2.7.0 :003 > foo.second
Traceback (most recent call last):
       16: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/friendly_errors.rb:123:in `with_friendly_errors'
       15: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/gems/2.7.0/gems/bundler-2.1.2/libexec/bundle:46:in `block in <top (required)>'
       14: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli.rb:24:in `start'
       13: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/vendor/thor/lib/thor/base.rb:476:in `start'
       12: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli.rb:30:in `dispatch'
       11: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/vendor/thor/lib/thor.rb:399:in `dispatch'
       10: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
        9: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
        8: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli.rb:476:in `exec'
        7: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli/exec.rb:28:in `run'
        6: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli/exec.rb:63:in `kernel_load'
        5: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/bundler/cli/exec.rb:63:in `load'
        4: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/bin/irb:23:in `<top (required)>'
        3: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/bin/irb:23:in `load'
        2: from /Users/sjohnson/.rvm/rubies/ruby-2.7.0/lib/ruby/gems/2.7.0/gems/irb-1.2.1/exe/irb:11:in `<top (required)>'
        1: from (irb):3
NoMethodError (undefined method `second' for []:Array)
Did you mean?  send