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ruby

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replace(res)
end
def flatten_once
dup.flatten_once!
end
end
----
=== Unused Variables Prefix [[underscore-unused-vars]]
Prefix with `+_+` unused block parameters and local variables.
It's also acceptable to use just `+_+` (although it's a bit less descriptive).
This convention is recognized by the Ruby interpreter and tools like RuboCop will suppress their unused variable warnings.
[source,ruby]
----
# bad
result = hash.map { |k, v| v + 1 }
def something(x)
unused_var, used_var = something_else(x)
# some code
end
# good
result = hash.map { |_k, v| v + 1 }
def something(x)
_unused_var, used_var = something_else(x)
# some code
end
# good
result = hash.map { |_, v| v + 1 }
def something(x)
_, used_var = something_else(x)
# some code
end
----
=== `other` Parameter [[other-arg]]
When defining binary operators and operator-alike methods, name the parameter `other` for operators with "symmetrical" semantics of operands.
Symmetrical semantics means both sides of the operator are typically of the same or coercible types.
Operators and operator-alike methods with symmetrical semantics (the parameter should be named `other`): `+`, `-`, `+*+`, `/`, `%`, `**`, `==`, `>`, `<`, `|`, `&`, `^`, `eql?`, `equal?`.
Operators with non-symmetrical semantics (the parameter should *not* be named `other`): `<<`, `[]` (collection/item relations between operands), `===` (pattern/matchable relations).
Note that the rule should be followed *only* if both sides of the operator have the same semantics.
Prominent exception in Ruby core is, for example, `Array#*(int)`.
[source,ruby]
----
# good
def +(other)
# body omitted
end
# bad
def <<(other)
@internal << other
end
# good
def <<(item)
@internal << item
end
# bad
# Returns some string multiplied `other` times
def *(other)
# body omitted
end
# good
# Returns some string multiplied `num` times
def *(num)
# body omitted
end
----
== Flow of Control
=== `for` Loops [[no-for-loops]]
Do not use `for`, unless you know exactly why.
Most of the time iterators should be used instead.
`for` is implemented in terms of `each` (so you're adding a level of indirection), but with a twist - `for` doesn't introduce a new scope (unlike `each`) and variables defined in its block will be visible outside it.
[source,ruby]
----
arr = [1, 2, 3]
# bad
for elem in arr do
puts elem
end