In Ruby, classes and modules are called constants. This card explains how Ruby resolves the meaning of a constant.

The good

E. g. in the following example, Array could mean either Foo::Array or simply Array:

class Foo
  def list
    Array.new
  end
end

What Ruby does here is to see if the name Array makes sense inside of Foo::, and if that fails, resolves it to ::Array (without a namespace).

The bad

You might be surprised that these are all valid ways to reference Ruby's String class:

…

On some machines, installing Ruby 1.8.7 with ruby-build can lead to this error:

math.c:37:13: error: missing binary operator before token "("

Try instead to install ruby-1.8.7-p374.

By convention, common protocols use a defined port, like 80 for HTTP or 443 for HTTPS.

You can use nmap to find out what service is running behind a given port, and most often see some details about it. This can be helpful if servers don't offer the services you expect for some ports. If you'd like to see what ports are listing on your local machine, you might want to use netstat instead of nmap.

Note that nmap's service discovery may trigger several requests.

Example

When using nmap, adding the -A switch …

RSpec provides a nice diff when certain matchers fail.

Here is an example where this diff is helpful while comparing two hashes:

{a:1}.should match(a:1, b:2)

Failure/Error: {a:1}.should match(a:1, b:2)
  expected {:a=>1} to match {:a=>1, :b=>2}
  Diff:
  @@ -1,3 +1,2 @@
   :a => 1,
  -:b => 2,

Unfortunately, this diff is not as clever as it would need to. RSpec's instance_of matchers will look like errors in the diff (even if they are not), and time objects that differ only in milliseconds won't appear in the …

Ruby has this handy block shortcut map(&:to_i) for map { |x| x.to_i }. However, it is limited to argument-less method invocations.

To call a method with an argument, you usually need to use the full block form. A common case is retrieving values from a list of hashes (imagine using a JSON API):

users = [ { name: 'Dominik', color: 'blue' }, { name: 'Stefan', color: 'red'} ]
names = users.collect do |user|
  user['name']
end

But with a little extension, you can do better.

Block shortcut with arguments

By defining `Symbol#c…

These steps are now part of Spreewald.

Here are some useful examples how to use the attached Cucumber Timecop steps:

When the date is 2011-05-06
When the time is 2011-05-06 17:30

There is also one really awesome step that lets you travel to the past or to the future:

When /^it is (\d+|a|some) (seconds?|minutes?|hours?|days?|months?|years?) (later|earlier)$/

As you can see, you describe the *time unit amo…

Expecting a primitive value as an argument to a method invocation is easy:

expect(object).to receive(:foo).with('arg1', 'arg2')

This expectation would be met with this call:

object.foo('arg1', 'arg2')

But what if the argument is expected to be an object with a given set of methods? E.g. this class with #first_name and #last_name methods:

class Person

  def initialize(first_name, last_name)
    @first_name = first_name
    @last_name = last_name
  end
  
  attr_reader :first_name, :last_name
  
end

To just t…

The 90s are calling: they want their tables back. Unfortunately, you'll need them all for laying out your HTML emails. (It is really that bad.)

Email client HTML rendering is way more scattered than browser HTML. While you might have a pretty good understanding of what features and patterns you can use to support all major browsers, I doubt anyone masters this craft for HTML email clients.

The only way to ensure your email looks good (acceptable, at least) in all mail clients, is to check it. Litmus is your go-to solu…

TLDR

• When counting records in an association, you should use #size in most cases.
• It will not work if the parent record has never been saved. Also there are finer distinctions between #size and #count. See below.

count

• Always makes a COUNT(*) query if a counter cache is not set up.
• If a counter cache is set up on the association, #count will return that cached value instead of executing a new query.

size, if the association has already been loaded

• Counts elements in the already loaded array.
• Does not …

Whenever is a Ruby gem that provides a nicer syntax for writing and deploying cron jobs.

Leading zeros are important for whenever if you use the 24-hours format!

This schedule.rb:

every 1.day, at: '3:00', roles: [:primary_cron] do
  runner 'Scheduler.delay.do_things'
end

will lead to this crontab entry (crontab -l):

0 15 * * * /bin/bash -l -c 'cd /var/www/my-project/releases/20180607182518 && bin/rails runner -e production '\''Scheduler.delay.do_things'\'''

Which would run on 3pm instead of 3am.

Using the l…

Using .downcase or .upcase on strings containing umlauts does not work as expected in Ruby versions before 2.4. It leaves the umlauts unchanged:

"Über".downcase
=> "Über"

"Ärger".downcase
=> "Ärger"

The very same applies for french accents (Thanks Guillaume!):

"Être ou ne pas être, telle est la question".downcase
=> "Être ou ne pas être, telle est la question"

Obviously, this leads to problems when comparing strings:

"Über".downcase == "über"
=> false

In Rails you can use ActiveSupports' [multib…

To make a local copy of an S3 bucket, I use the s3cmd command line tool.

Configure access keys:

s3cmd --configure

Make a local directory for the backup:

mkdir s3backup
cd s3backup

Get a preview of what we're going to copy:

s3cmd sync --dry-run s3://your-bucket-name-here .

Start copying files:

s3cmd sync s3://your-bucket-name-here .

In a nutshell: Use git rebase source-commit --onto target-branch

• target-branch means "branch you want to be based on"
• source-commit means "commit before your first feature commit"

Let's say my-feature-branch is based on master and we want it to be based on production. Consider this history (topmost = latest):

• commit 6 [my-feature-branch]
• commit 5
• commit 4 [master]
• commit 3
• commit 2 [production]
• commit 1

Here, master has commits that are not yet in production (number 3 and 4).

J…

Rails defines a #truncate helper as well as a method String#truncate.

= truncate("my string", length: 5)
= "my string".truncate(5)

Both are really similar; in fact, the helper invokes the method and improves it with two niceties: support for passing a block (which could e.g. render a "read on" link), and html_safe knowledge.

Prefer the truncate() helper

The method knows nothing about html_safe and will always return an unsafe string. FWIW, an HTML string may easily become invalid when truncated, e.g. when a closing ta…

To catch all possible exceptions from a network call, we need to rescue many error classes like this:

rescue SocketError, Errno::ECONNREFUSED, Errno::ECONNRESET, Errno::ECONNABORTED, Errno::EHOSTUNREACH, OpenSSL::SSL::SSLError, MyHttpLib::BadResponse

You can shorten this a bit by rescuing SystemCallError, which is a base class for all Errno:: exceptions:

rescue SocketError, SystemCallError, OpenSSL::SSL::SSLError, MyHttpLib::BadResponse

Some high-level …