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ruby

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Use `def` with parentheses when there are parameters.
Omit the parentheses when the method doesn't accept any parameters.
[source,ruby]
----
# bad
def some_method()
# body omitted
end
# good
def some_method
# body omitted
end
# bad
def some_method_with_parameters param1, param2
# body omitted
end
# good
def some_method_with_parameters(param1, param2)
# body omitted
end
----
=== Method Call Parentheses [[method-invocation-parens]][[method-call-parens]]
Use parentheses around the arguments of method calls, especially if the first argument begins with an open parenthesis `(`, as in `f((3 + 2) + 1)`.
[source,ruby]
----
# bad
x = Math.sin y
# good
x = Math.sin(y)
# bad
array.delete e
# good
array.delete(e)
# bad
temperance = Person.new 'Temperance', 30
# good
temperance = Person.new('Temperance', 30)
----
==== Method Call with No Arguments [[method-invocation-parens-no-args]][[method-call-parens-no-args]]
Always omit parentheses for method calls with no arguments.
[source,ruby]
----
# bad
Kernel.exit!()
2.even?()
fork()
'test'.upcase()
# good
Kernel.exit!
2.even?
fork
'test'.upcase
----
==== Methods That are Part of an Internal DSL [[method-invocation-parens-internal-dsl]][[method-call-parens-internal-dsl]]
Always omit parentheses for methods that are part of an internal DSL (e.g., Rake, Rails, RSpec):
[source,ruby]
----
# bad
validates(:name, presence: true)
# good
validates :name, presence: true
----
==== Methods That Have "keyword" Status in Ruby [[method-invocation-parens-keyword]][[method-call-parens-keyword]]
Always omit parentheses for methods that have "keyword" status in Ruby.
NOTE: Unfortunately, it's not exactly clear _which_ methods have "keyword" status.
There is agreement that declarative methods have "keyword" status.
However, there's less agreement on which non-declarative methods, if any, have "keyword" status.
===== Declarative Methods That Have "keyword" Status in Ruby [[method-invocation-parens-declarative-keyword]][[method-call-parens-declarative-keyword]]
Always omit parentheses for declarative methods (a.k.a. DSL methods or macro methods) that have "keyword" status in Ruby (e.g., various `Module` instance methods):
[source,ruby]
----
class Person
# bad
attr_reader(:name, :age)
# good
attr_reader :name, :age
# body omitted