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

Checks hash literal syntax.

It can enforce either the use of the class hash rocket syntax or the use of the newer Ruby 1.9 syntax (when applicable).

A separate offense is registered for each problematic pair.

The supported styles are:

• ruby19 - forces use of the 1.9 syntax (e.g. {a: 1}) when hashes have all symbols for keys
• hash_rockets - forces use of hash rockets for all hashes
• nomixedkeys - simply checks for hashes with mixed syntaxes
• ruby19nomixed_keys - forces use of ruby 1.9 syntax and forbids mixed syntax hashes

This cop has EnforcedShorthandSyntax option. It can enforce either the use of the explicit hash value syntax or the use of Ruby 3.1's hash value shorthand syntax.

The supported styles are:

• always - forces use of the 3.1 syntax (e.g. {foo:})
• never - forces use of explicit hash literal value
• either - accepts both shorthand and explicit use of hash literal value

Example: EnforcedStyle: ruby19 (default)

# bad
{:a => 2}
{b: 1, :c => 2}

# good
{a: 2, b: 1}
{:c => 2, 'd' => 2} # acceptable since 'd' isn't a symbol
{d: 1, 'e' => 2} # technically not forbidden

Example: EnforcedStyle: hash_rockets

# bad
{a: 1, b: 2}
{c: 1, 'd' => 5}

# good
{:a => 1, :b => 2}

Example: EnforcedStyle: nomixedkeys

# bad
{:a => 1, b: 2}
{c: 1, 'd' => 2}

# good
{:a => 1, :b => 2}
{c: 1, d: 2}

Example: EnforcedStyle: ruby19nomixed_keys

# bad
{:a => 1, :b => 2}
{c: 2, 'd' => 3} # should just use hash rockets

# good
{a: 1, b: 2}
{:c => 3, 'd' => 4}

Example: EnforcedShorthandSyntax: always (default)

# bad
{foo: foo, bar: bar}

# good
{foo:, bar:}

Example: EnforcedShorthandSyntax: never

# bad
{foo:, bar:}

# good
{foo: foo, bar: bar}

Example: EnforcedShorthandSyntax: either

# good
{foo: foo, bar: bar}

# good
{foo:, bar:}

Makes sure that rescued exceptions variables are named as expected.

The PreferredName config option takes a String. It represents the required name of the variable. Its default is e.

NOTE: This cop does not consider nested rescues because it cannot guarantee that the variable from the outer rescue is not used within the inner rescue (in which case, changing the inner variable would shadow the outer variable).

Example: PreferredName: e (default)

# bad
begin
  # do something
rescue MyException => exception
  # do something
end

# good
begin
  # do something
rescue MyException => e
  # do something
end

# good
begin
  # do something
rescue MyException => _e
  # do something
end

Example: PreferredName: exception

# bad
begin
  # do something
rescue MyException => e
  # do something
end

# good
begin
  # do something
rescue MyException => exception
  # do something
end

# good
begin
  # do something
rescue MyException => _exception
  # do something
end

Check for uses of braces or do/end around single line or multi-line blocks.

Methods that can be either procedural or functional and cannot be categorised from their usage alone is ignored. lambda, proc, and it are their defaults. Additional methods can be added to the IgnoredMethods.

Example: EnforcedStyle: linecountbased (default)

# bad - single line block
items.each do |item| item / 5 end

# good - single line block
items.each { |item| item / 5 }

# bad - multi-line block
things.map { |thing|
  something = thing.some_method
  process(something)
}

# good - multi-line block
things.map do |thing|
  something = thing.some_method
  process(something)
end

Example: EnforcedStyle: semantic

# Prefer `do...end` over `{...}` for procedural blocks.

# return value is used/assigned
# bad
foo = map do |x|
  x
end
puts (map do |x|
  x
end)

# return value is not used out of scope
# good
map do |x|
  x
end

# Prefer `{...}` over `do...end` for functional blocks.

# return value is not used out of scope
# bad
each { |x|
  x
}

# return value is used/assigned
# good
foo = map { |x|
  x
}
map { |x|
  x
}.inspect

# The AllowBracesOnProceduralOneLiners option is ignored unless the
# EnforcedStyle is set to `semantic`. If so:

# If the AllowBracesOnProceduralOneLiners option is unspecified, or
# set to `false` or any other falsey value, then semantic purity is
# maintained, so one-line procedural blocks must use do-end, not
# braces.

# bad
collection.each { |element| puts element }

# good
collection.each do |element| puts element end

# If the AllowBracesOnProceduralOneLiners option is set to `true`, or
# any other truthy value, then one-line procedural blocks may use
# either style. (There is no setting for requiring braces on them.)

# good
collection.each { |element| puts element }

# also good
collection.each do |element| puts element end

Example: EnforcedStyle: bracesforchaining

# bad
words.each do |word|
  word.flip.flop
end.join("-")

# good
words.each { |word|
  word.flip.flop
}.join("-")

Example: EnforcedStyle: always_braces

# bad
words.each do |word|
  word.flip.flop
end

# good
words.each { |word|
  word.flip.flop
}

Example: BracesRequiredMethods: ['sig']

# Methods listed in the BracesRequiredMethods list, such as 'sig'
# in this example, will require `{...}` braces. This option takes
# precedence over all other configurations except IgnoredMethods.

# bad
sig do
  params(
    foo: string,
  ).void
end
def bar(foo)
  puts foo
end

# good
sig {
  params(
    foo: string,
  ).void
}
def bar(foo)
  puts foo
end

Example: IgnoredMethods: ['lambda', 'proc', 'it' ] (default)

# good
foo = lambda do |x|
  puts "Hello, #{x}"
end

foo = lambda do |x|
  x * 100
end

Checks hash literal syntax.

It can enforce either the use of the class hash rocket syntax or the use of the newer Ruby 1.9 syntax (when applicable).

A separate offense is registered for each problematic pair.

The supported styles are:

• ruby19 - forces use of the 1.9 syntax (e.g. {a: 1}) when hashes have all symbols for keys
• hash_rockets - forces use of hash rockets for all hashes
• nomixedkeys - simply checks for hashes with mixed syntaxes
• ruby19nomixed_keys - forces use of ruby 1.9 syntax and forbids mixed syntax hashes

This cop has EnforcedShorthandSyntax option. It can enforce either the use of the explicit hash value syntax or the use of Ruby 3.1's hash value shorthand syntax.

The supported styles are:

• always - forces use of the 3.1 syntax (e.g. {foo:})
• never - forces use of explicit hash literal value
• either - accepts both shorthand and explicit use of hash literal value

Example: EnforcedStyle: ruby19 (default)

# bad
{:a => 2}
{b: 1, :c => 2}

# good
{a: 2, b: 1}
{:c => 2, 'd' => 2} # acceptable since 'd' isn't a symbol
{d: 1, 'e' => 2} # technically not forbidden

Example: EnforcedStyle: hash_rockets

# bad
{a: 1, b: 2}
{c: 1, 'd' => 5}

# good
{:a => 1, :b => 2}

Example: EnforcedStyle: nomixedkeys

# bad
{:a => 1, b: 2}
{c: 1, 'd' => 2}

# good
{:a => 1, :b => 2}
{c: 1, d: 2}

Example: EnforcedStyle: ruby19nomixed_keys

# bad
{:a => 1, :b => 2}
{c: 2, 'd' => 3} # should just use hash rockets

# good
{a: 1, b: 2}
{:c => 3, 'd' => 4}

Example: EnforcedShorthandSyntax: always (default)

# bad
{foo: foo, bar: bar}

# good
{foo:, bar:}

Example: EnforcedShorthandSyntax: never

# bad
{foo:, bar:}

# good
{foo: foo, bar: bar}

Example: EnforcedShorthandSyntax: either

# good
{foo: foo, bar: bar}

# good
{foo:, bar:}

Checks hash literal syntax.

It can enforce either the use of the class hash rocket syntax or the use of the newer Ruby 1.9 syntax (when applicable).

A separate offense is registered for each problematic pair.

The supported styles are:

• ruby19 - forces use of the 1.9 syntax (e.g. {a: 1}) when hashes have all symbols for keys
• hash_rockets - forces use of hash rockets for all hashes
• nomixedkeys - simply checks for hashes with mixed syntaxes
• ruby19nomixed_keys - forces use of ruby 1.9 syntax and forbids mixed syntax hashes

This cop has EnforcedShorthandSyntax option. It can enforce either the use of the explicit hash value syntax or the use of Ruby 3.1's hash value shorthand syntax.

The supported styles are:

• always - forces use of the 3.1 syntax (e.g. {foo:})
• never - forces use of explicit hash literal value
• either - accepts both shorthand and explicit use of hash literal value

Example: EnforcedStyle: ruby19 (default)

# bad
{:a => 2}
{b: 1, :c => 2}

# good
{a: 2, b: 1}
{:c => 2, 'd' => 2} # acceptable since 'd' isn't a symbol
{d: 1, 'e' => 2} # technically not forbidden

Example: EnforcedStyle: hash_rockets

# bad
{a: 1, b: 2}
{c: 1, 'd' => 5}

# good
{:a => 1, :b => 2}

Example: EnforcedStyle: nomixedkeys

# bad
{:a => 1, b: 2}
{c: 1, 'd' => 2}

# good
{:a => 1, :b => 2}
{c: 1, d: 2}

Example: EnforcedStyle: ruby19nomixed_keys

# bad
{:a => 1, :b => 2}
{c: 2, 'd' => 3} # should just use hash rockets

# good
{a: 1, b: 2}
{:c => 3, 'd' => 4}

Example: EnforcedShorthandSyntax: always (default)

# bad
{foo: foo, bar: bar}

# good
{foo:, bar:}

Example: EnforcedShorthandSyntax: never

# bad
{foo:, bar:}

# good
{foo: foo, bar: bar}

Example: EnforcedShorthandSyntax: either

# good
{foo: foo, bar: bar}

# good
{foo:, bar:}