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# good
SOME_CONST = 5
----
=== Predicate Methods Suffix [[bool-methods-qmark]]
The names of predicate methods (methods that return a boolean value) should end in a question mark (i.e. `Array#empty?`).
Methods that don't return a boolean, shouldn't end in a question mark.
[source,ruby]
----
# bad
def even(value)
end
# good
def even?(value)
end
----
=== Predicate Methods Prefix [[bool-methods-prefix]]
Avoid prefixing predicate methods with the auxiliary verbs such as `is`, `does`, or `can`.
These words are redundant and inconsistent with the style of boolean methods in the Ruby core library, such as `empty?` and `include?`.
[source,ruby]
----
# bad
class Person
def is_tall?
true
end
def can_play_basketball?
false
end
def does_like_candy?
true
end
end
# good
class Person
def tall?
true
end
def basketball_player?
false
end
def likes_candy?
true
end
end
----
=== Dangerous Method Suffix [[dangerous-method-bang]]
The names of potentially _dangerous_ methods (i.e. methods that modify `self` or the arguments, `exit!` (doesn't run the finalizers like `exit` does), etc) should end with an exclamation mark if there exists a safe version of that _dangerous_ method.
[source,ruby]
----
# bad - there is no matching 'safe' method
class Person
def update!
end
end
# good
class Person
def update
end
end
# good
class Person
def update!
end
def update
end
end
----
=== Relationship between Safe and Dangerous Methods [[safe-because-unsafe]]
Define the non-bang (safe) method in terms of the bang (dangerous) one if possible.
[source,ruby]
----
class Array
def flatten_once!
res = []
each do |e|
[*e].each { |f| res << f }
end