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NOTE: Whether organizing control flow with `and` and `or` is a good idea has been a controversial topic in the community for a long time. But if you do, prefer these operators over `&&`/`||`. As the different operators are meant to have different semantics that makes it easier to reason whether you're dealing with a logical expression (that will get reduced to a boolean value) or with flow of control.
.Why is using `and` and `or` as logical operators a bad idea?
****
Simply put - because they add some cognitive overhead, as they don't behave like similarly named logical operators in other languages.
First of all, `and` and `or` operators have lower precedence than the `=` operator, whereas the `&&` and `||` operators have higher precedence than the `=` operator, based on order of operations.
[source,ruby]
----
foo = true and false # results in foo being equal to true. Equivalent to (foo = true) and false
bar = false or true # results in bar being equal to false. Equivalent to (bar = false) or true
----
Also `&&` has higher precedence than `||`, where as `and` and `or` have the same one. Funny enough, even though `and` and `or`
were inspired by Perl, they don't have different precedence in Perl.
[source,ruby]
----
true or true and false # => false (it's effectively (true or true) and false)
true || true && false # => true (it's effectively true || (true && false)
false or true and false # => false (it's effectively (false or true) and false)
false || true && false # => false (it's effectively false || (true && false))
----
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=== Multi-line Ternary Operator [[no-multiline-ternary]]
Avoid multi-line `?:` (the ternary operator); use `if`/`unless` instead.
=== `if` as a Modifier [[if-as-a-modifier]]
Prefer modifier `if`/`unless` usage when you have a single-line body.
Another good alternative is the usage of control flow `&&`/`||`.
[source,ruby]
----
# bad
if some_condition
do_something
end
# good
do_something if some_condition
# another good option
some_condition && do_something
----
=== Multi-line `if` Modifiers [[no-multiline-if-modifiers]]
Avoid modifier `if`/`unless` usage at the end of a non-trivial multi-line block.
[source,ruby]
----
# bad
10.times do
# multi-line body omitted
end if some_condition
# good
if some_condition
10.times do
# multi-line body omitted
end
end
----
=== Nested Modifiers [[no-nested-modifiers]]
Avoid nested modifier `if`/`unless`/`while`/`until` usage.
Prefer `&&`/`||` if appropriate.
[source,ruby]
----
# bad
do_something if other_condition if some_condition
# good
do_something if some_condition && other_condition
----
=== `if` vs `unless` [[unless-for-negatives]]
Prefer `unless` over `if` for negative conditions (or control flow `||`).
[source,ruby]
----
# bad
do_something if !some_condition
# bad
do_something if not some_condition
# good
do_something unless some_condition
# another good option
some_condition || do_something
----