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

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

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 identifies places where $stderr.puts can be replaced by warn. The latter has the advantage of easily being disabled by, e.g. the -W0 interpreter flag, or setting $VERBOSE to nil.

Example:

# bad
$stderr.puts('hello')

# good
warn('hello')

Checks for uses of if/unless modifiers with multiple-lines bodies.

Example:

# bad
{
  result: 'this should not happen'
} unless cond

# good
{ result: 'ok' } if cond

This cop enforces the consistent usage of %-literal delimiters.

Specify the 'default' key to set all preferred delimiters at once. You can continue to specify individual preferred delimiters to override the default.

Example:

# Style/PercentLiteralDelimiters:
#   PreferredDelimiters:
#     default: '[]'
#     '%i':    '()'

# good
%w[alpha beta] + %i(gamma delta)

# bad
%W(alpha #{beta})

# bad
%I(alpha beta)

Checks for a newline after the final magic comment.

Example:

# good
# frozen_string_literal: true

# Some documentation for Person
class Person
  # Some code
end

# bad
# frozen_string_literal: true
# Some documentation for Person
class Person
  # Some code
end

This cop checks for usage of comparison operators (==, >, <) to test numbers as zero, positive, or negative. These can be replaced by their respective predicate methods. The cop can also be configured to do the reverse.

The cop disregards #nonzero? as it its value is truthy or falsey, but not true and false, and thus not always interchangeable with != 0.

The cop ignores comparisons to global variables, since they are often populated with objects which can be compared with integers, but are not themselves Interger polymorphic.

Example: EnforcedStyle: predicate (default)

# bad

foo == 0
0 > foo
bar.baz > 0

# good

foo.zero?
foo.negative?
bar.baz.positive?

Example: EnforcedStyle: comparison

# bad

foo.zero?
foo.negative?
bar.baz.positive?

# good

foo == 0
0 > foo
bar.baz > 0

Checks for uses of if/unless modifiers with multiple-lines bodies.

Example:

# bad
{
  result: 'this should not happen'
} unless cond

# good
{ result: 'ok' } if cond

This cop checks for Yoda conditions, i.e. comparison operations where readability is reduced because the operands are not ordered the same way as they would be ordered in spoken English.

Example: EnforcedStyle: allcomparisonoperators (default)

# bad
99 == foo
"bar" != foo
42 >= foo
10 < bar

# good
foo == 99
foo == "bar"
foo <= 42
bar > 10

Example: EnforcedStyle: equalityoperatorsonly

# bad
99 == foo
"bar" != foo

# good
99 >= foo
3 < a && a < 5

Dependencies in the gemspec should be alphabetically sorted.

Example:

# bad
spec.add_dependency 'rubocop'
spec.add_dependency 'rspec'

# good
spec.add_dependency 'rspec'
spec.add_dependency 'rubocop'

# good
spec.add_dependency 'rubocop'

spec.add_dependency 'rspec'

# bad
spec.add_development_dependency 'rubocop'
spec.add_development_dependency 'rspec'

# good
spec.add_development_dependency 'rspec'
spec.add_development_dependency 'rubocop'

# good
spec.add_development_dependency 'rubocop'

spec.add_development_dependency 'rspec'

# bad
spec.add_runtime_dependency 'rubocop'
spec.add_runtime_dependency 'rspec'

# good
spec.add_runtime_dependency 'rspec'
spec.add_runtime_dependency 'rubocop'

# good
spec.add_runtime_dependency 'rubocop'

spec.add_runtime_dependency 'rspec'

# good only if TreatCommentsAsGroupSeparators is true
# For code quality
spec.add_dependency 'rubocop'
# For tests
spec.add_dependency 'rspec'

Checks for a newline after the final magic comment.

Example:

# good
# frozen_string_literal: true

# Some documentation for Person
class Person
  # Some code
end

# bad
# frozen_string_literal: true
# Some documentation for Person
class Person
  # Some code
end

Checks for uses of if/unless modifiers with multiple-lines bodies.

Example:

# bad
{
  result: 'this should not happen'
} unless cond

# good
{ result: 'ok' } if cond

This cop identifies places where $stderr.puts can be replaced by warn. The latter has the advantage of easily being disabled by, e.g. the -W0 interpreter flag, or setting $VERBOSE to nil.

Example:

# bad
$stderr.puts('hello')

# good
warn('hello')