This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

This cop checks for extra/unnecessary whitespace.

Example:

# good if AllowForAlignment is true
name      = "RuboCop"
# Some comment and an empty line

website  += "/bbatsov/rubocop" unless cond
puts        "rubocop"          if     debug

# bad for any configuration
set_app("RuboCop")
website  = "https://github.com/bbatsov/rubocop"

This cop checks for redundant return expressions.

Example:

def test
  return something
end

def test
  one
  two
  three
  return something
end

It should be extended to handle methods whose body is if/else or a case expression with a default branch.

Checks if uses of quotes match the configured preference.

Example: EnforcedStyle: single_quotes (default)

# bad
"No special symbols"
"No string interpolation"
"Just text"

# good
'No special symbols'
'No string interpolation'
'Just text'
"Wait! What's #{this}!"

Example: EnforcedStyle: double_quotes

# bad
'Just some text'
'No special chars or interpolation'

# good
"Just some text"
"No special chars or interpolation"
"Every string in #{project} uses double_quotes"

This cop checks for trailing comma in array and hash literals.

Example: EnforcedStyleForMultiline: consistent_comma

# bad
a = [1, 2,]

# good
a = [
  1, 2,
  3,
]

# good
a = [
  1,
  2,
]

Example: EnforcedStyleForMultiline: comma

# bad
a = [1, 2,]

# good
a = [
  1,
  2,
]

Example: EnforcedStyleForMultiline: no_comma (default)

# bad
a = [1, 2,]

# good
a = [
  1,
  2
]