This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

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 cops checks if empty lines exist around the bodies of begin sections. This cop doesn't check empty lines at begin body beginning/end and around method definition body. Style/EmptyLinesAroundBeginBody or Style/EmptyLinesAroundMethodBody can be used for this purpose.

Example:

# good

begin
  do_something
rescue
  do_something2
else
  do_something3
ensure
  do_something4
end

# good

def foo
  do_something
rescue
  do_something2
end

# bad

begin
  do_something

rescue

  do_something2

else

  do_something3

ensure

  do_something4
end

# bad

def foo
  do_something

rescue

  do_something2
end

This cops checks if empty lines exist around the bodies of begin sections. This cop doesn't check empty lines at begin body beginning/end and around method definition body. Style/EmptyLinesAroundBeginBody or Style/EmptyLinesAroundMethodBody can be used for this purpose.

Example:

# good

begin
  do_something
rescue
  do_something2
else
  do_something3
ensure
  do_something4
end

# good

def foo
  do_something
rescue
  do_something2
end

# bad

begin
  do_something

rescue

  do_something2

else

  do_something3

ensure

  do_something4
end

# bad

def foo
  do_something

rescue

  do_something2
end

This cop checks that the closing brace in a method call is either on the same line as the last method argument, or a new line.

When using the symmetrical (default) style:

If a method call's opening brace is on the same line as the first argument of the call, then the closing brace should be on the same line as the last argument of the call.

If an method call's opening brace is on the line above the first argument of the call, then the closing brace should be on the line below the last argument of the call.

When using the new_line style:

The closing brace of a multi-line method call must be on the line after the last argument of the call.

When using the same_line style:

The closing brace of a multi-line method call must be on the same line as the last argument of the call.

Example:

# symmetrical: bad
  # new_line: good
  # same_line: bad
  foo(a,
    b
  )

  # symmetrical: bad
  # new_line: bad
  # same_line: good
  foo(
    a,
    b)

  # symmetrical: good
  # new_line: bad
  # same_line: good
  foo(a,
    b)

  # symmetrical: good
  # new_line: good
  # same_line: bad
  foo(
    a,
    b
  )

This cop checks for the presence of parentheses around ternary conditions. It is configurable to enforce inclusion or omission of parentheses using EnforcedStyle. Omission is only enforced when removing the parentheses won't cause a different behavior.

Example: EnforcedStyle: requirenoparentheses (default)

# bad
foo = (bar?) ? a : b
foo = (bar.baz?) ? a : b
foo = (bar && baz) ? a : b

# good
foo = bar? ? a : b
foo = bar.baz? ? a : b
foo = bar && baz ? a : b

Example: EnforcedStyle: require_parentheses

# bad
foo = bar? ? a : b
foo = bar.baz? ? a : b
foo = bar && baz ? a : b

# good
foo = (bar?) ? a : b
foo = (bar.baz?) ? a : b
foo = (bar && baz) ? a : b

Example: EnforcedStyle: requireparentheseswhen_complex

# bad
foo = (bar?) ? a : b
foo = (bar.baz?) ? a : b
foo = bar && baz ? a : b

# good
foo = bar? ? a : b
foo = bar.baz? ? a : b
foo = (bar && baz) ? a : b

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 cops checks if empty lines exist around the bodies of begin sections. This cop doesn't check empty lines at begin body beginning/end and around method definition body. Style/EmptyLinesAroundBeginBody or Style/EmptyLinesAroundMethodBody can be used for this purpose.

Example:

# good

begin
  do_something
rescue
  do_something2
else
  do_something3
ensure
  do_something4
end

# good

def foo
  do_something
rescue
  do_something2
end

# bad

begin
  do_something

rescue

  do_something2

else

  do_something3

ensure

  do_something4
end

# bad

def foo
  do_something

rescue

  do_something2
end

This cop checks for rescue blocks with no body.

Example:

# bad

def some_method
  do_something
rescue
  # do nothing
end

Example:

# bad

begin
  do_something
rescue
  # do nothing
end

Example:

# good

def some_method
  do_something
rescue
  handle_exception
end

Example:

# good

begin
  do_something
rescue
  handle_exception
end

Check for arguments to rescue that will result in a TypeError if an exception is raised.

Example:

# bad
begin
  bar
rescue nil
  baz
end

# bad
def foo
  bar
rescue 1, 'a', "#{b}", 0.0, [], {}
  baz
end

# good
begin
  bar
rescue
  baz
end

# good
def foo
  bar
rescue NameError
  baz
end

This cops checks if empty lines exist around the bodies of begin sections. This cop doesn't check empty lines at begin body beginning/end and around method definition body. Style/EmptyLinesAroundBeginBody or Style/EmptyLinesAroundMethodBody can be used for this purpose.

Example:

# good

begin
  do_something
rescue
  do_something2
else
  do_something3
ensure
  do_something4
end

# good

def foo
  do_something
rescue
  do_something2
end

# bad

begin
  do_something

rescue

  do_something2

else

  do_something3

ensure

  do_something4
end

# bad

def foo
  do_something

rescue

  do_something2
end

This cops checks if empty lines exist around the bodies of begin sections. This cop doesn't check empty lines at begin body beginning/end and around method definition body. Style/EmptyLinesAroundBeginBody or Style/EmptyLinesAroundMethodBody can be used for this purpose.

Example:

# good

begin
  do_something
rescue
  do_something2
else
  do_something3
ensure
  do_something4
end

# good

def foo
  do_something
rescue
  do_something2
end

# bad

begin
  do_something

rescue

  do_something2

else

  do_something3

ensure

  do_something4
end

# bad

def foo
  do_something

rescue

  do_something2
end

This cop checks that the closing brace in a hash literal is either on the same line as the last hash element, or a new line.

When using the symmetrical (default) style:

If a hash's opening brace is on the same line as the first element of the hash, then the closing brace should be on the same line as the last element of the hash.

If a hash's opening brace is on the line above the first element of the hash, then the closing brace should be on the line below the last element of the hash.

When using the new_line style:

The closing brace of a multi-line hash literal must be on the line after the last element of the hash.

When using the same_line style:

The closing brace of a multi-line hash literal must be on the same line as the last element of the hash.

Example: EnforcedStyle: symmetrical (default)

# bad
  { a: 1,
    b: 2
  }
  # bad
  {
    a: 1,
    b: 2 }

  # good
  { a: 1,
    b: 2 }

  # good
  {
    a: 1,
    b: 2
  }

Example: EnforcedStyle: new_line

# bad
  {
    a: 1,
    b: 2 }

  # bad
  { a: 1,
    b: 2 }

  # good
  { a: 1,
    b: 2
  }

  # good
  {
    a: 1,
    b: 2
  }

Example: EnforcedStyle: same_line

# bad
  { a: 1,
    b: 2
  }

  # bad
  {
    a: 1,
    b: 2
  }

  # good
  {
    a: 1,
    b: 2 }

  # good
  { a: 1,
    b: 2 }

This cop checks for a rescued exception that get shadowed by a less specific exception being rescued before a more specific exception is rescued.

Example:

# bad

begin
  something
rescue Exception
  handle_exception
rescue StandardError
  handle_standard_error
end

# good

begin
  something
rescue StandardError
  handle_standard_error
rescue Exception
  handle_exception
end

# good, however depending on runtime environment.
#
# This is a special case for system call errors.
# System dependent error code depends on runtime environment.
# For example, whether `Errno::EAGAIN` and `Errno::EWOULDBLOCK` are
# the same error code or different error code depends on environment.
# This good case is for `Errno::EAGAIN` and `Errno::EWOULDBLOCK` with
# the same error code.
begin
  something
rescue Errno::EAGAIN, Errno::EWOULDBLOCK
  handle_standard_error
end

This cops checks if empty lines exist around the bodies of begin sections. This cop doesn't check empty lines at begin body beginning/end and around method definition body. Style/EmptyLinesAroundBeginBody or Style/EmptyLinesAroundMethodBody can be used for this purpose.

Example:

# good

begin
  do_something
rescue
  do_something2
else
  do_something3
ensure
  do_something4
end

# good

def foo
  do_something
rescue
  do_something2
end

# bad

begin
  do_something

rescue

  do_something2

else

  do_something3

ensure

  do_something4
end

# bad

def foo
  do_something

rescue

  do_something2
end