Ruby Monstas

Formatting your code

Motivation

Code formatting is important. It will help you to read and understand your code better.

Your brain is a pattern recognition machine. If you properly format your code you train your brain to subconciously recognise patterns of correct vs. incorrect code.

Thus it will also help you find bugs!

Compare these 2 pieces of code: 

  def widths (     row
)
 row.map do | cell| cell.width
end
     end
def widths(row)
  row.map do |cell|
    cell.width
  end
end

Which is easier to read and understand?

Indentation

Proper indentation is the most important aspect of formatting your code

If you follow the following 2 rules, your code will be properly indented.

Don't worry: After a while these rules will be obvious and you will intuitively follow them.

Rule 1

Whenever you have one of these keywords, then the lines following it are indented one level deeper:

if
elsif
else
do
def

The same applies for these keywords which we haven't encountered yet:

unless
while
until
case
class
module
begin
rescue
ensure

Rule 2

Whenever you have one of these keywords, then that line is indented one level less deep:

elsif
else
end

The same applies for these keywords which we haven't encountered yet:

when
rescue
ensure

Example

Let's properly indent this code, line by line:

def widths(row)
row.map do |cell|
cell.width
end
end

For line 1, we don't need to do anything. It's stays indented 0 levels (top level):

def widths(row)
row.map do |cell|
cell.width
end
end
But, for line 1, Rule 1 applies, because it contains a 
def
. So we need to indent the following lines by +1 level (one level deeper):
def widths(row)
  row.map do |cell|
  cell.width
  end
  end
On line 2 we have a 
do
, so Rule 1 applies again: we indent the following lines by +1 level (one level deeper):
def widths(row)
  row.map do |cell|
    cell.width
    end
    end
On line 3 there is no keyword. So neither of the rules apply and we leave it as is:
def widths(row)
  row.map do |cell|
    cell.width
    end
    end
Line 4 has an 
end
. Here we need to use Rule 2, which says that it gets indented one level less deep (-1 level) than the previous line:
def widths(row)
  row.map do |cell|
    cell.width
  end
    end
On line 5 the same rule applies again: We indent it one level less deep (-1 level) than the previous line:
def widths(row)
  row.map do |cell|
    cell.width
  end
end

And we're done!

Interactive exercise

Let's exercise the rules together with another example:

def judge_weather(weather)
if weather == "sunny"
puts "The weather is great!"
3.times do
puts "Yes!"
end
elsif weather == "rainy"
puts "Better stay inside..."
end
end

Pattern recognition

If done correctly, indentation lets you see immediately which lines of code belong together and which don't:

def judge_weather(weather)
  if weather == "sunny"
    puts "The weather is great!"
    3.times do
      puts "Yes!"
    end
  elsif weather == "rainy"
    puts "Better stay inside..."
  end
end
Here you can see easily that lines 3-6 are executed only if the 
weather
is "sunny".
It's not uncommon to have many nested levels. Sometimes this results in a lot of 
end
s at the bottom of your file:

def ...
  if ...
    do
      if ...
        if ...
          ...
        end
      end
    end
  end
end

Hints

Avoid skipping indentation levels from one line to the other: 

array.each do |element|
    if element.start_with?("A")
      puts element
    end
end

This is bad: Lines 2-4 are indented by 2 levels instead of 1!

Let your editor help you. It automatically increases and decreases indentation levels when you use a keyword.

Try it now! Type the following in your editor: 

def my_method

And hit the enter key. Your cursor will automatically be indented by one level on the next line.

Now type 
end
. Your editor will automatically unindent that line for you: 
def my_method
end

Use Tab and Shift + Tab to indent and unindent lines respectively.

This also works with multiple lines at once. Try it now!

Make this a habit: Whenever you type a keyword that needs an 
end
, immediately type that on the next line. This way you never have too many or too few 
end
s!

If you use indentation correctly, your editor allows you to expand and collapse code sections. Try clicking the little triangle that appears next to the line numbers!

Further information

The "official" Ruby style guide has more information on code formatting as well as which Ruby features to use or not use:

rubystyle.guide

Additional Resources

Ruby For Beginners: Formatting your code

What questions do you have?