What is the difference between the &&
and and
operators in Ruby?
7 Answers
and
is the same as &&
but with lower precedence. They both use short-circuit evaluation.
WARNING: and
even has lower precedence than =
so you'll usually want to avoid and
. An example when and
should be used can be found in the Rails Guide under "Avoiding Double Render Errors".
The practical difference is binding strength, which can lead to peculiar behavior if you're not prepared for it:
foo = :foo
bar = nil
a = foo and bar
# => nil
a
# => :foo
a = foo && bar
# => nil
a
# => nil
a = (foo and bar)
# => nil
a
# => nil
(a = foo) && bar
# => nil
a
# => :foo
The same thing works for ||
and or
.
The Ruby Style Guide says it better than I could:
Use &&/|| for boolean expressions, and/or for control flow. (Rule of thumb: If you have to use outer parentheses, you are using the wrong operators.)
# boolean expression
if some_condition && some_other_condition
do_something
end
# control flow
document.saved? or document.save!
||
and &&
bind with the precedence that you expect from boolean operators in programming languages (&&
is very strong, ||
is slightly less strong).
and
and or
have lower precedence.
For example, unlike ||
, or
has lower precedence than =
:
> a = false || true
=> true
> a
=> true
> a = false or true
=> true
> a
=> false
Likewise, unlike &&
, and
also has lower precedence than =
:
> a = true && false
=> false
> a
=> false
> a = true and false
=> false
> a
=> true
What's more, unlike &&
and ||
, and
and or
bind with equal precedence:
> !puts(1) || !puts(2) && !puts(3)
1
=> true
> !puts(1) or !puts(2) and !puts(3)
1
3
=> true
> !puts(1) or (!puts(2) and !puts(3))
1
=> true
The weakly-binding and
and or
may be useful for control-flow purposes: see http://devblog.avdi.org/2010/08/02/using-and-and-or-in-ruby/ .
and
has lower precedence than &&
.
But for an unassuming user, problems might occur if it is used along with other operators whose precedence are in between, for example, the assignment operator:
def happy?() true; end
def know_it?() true; end
todo = happy? && know_it? ? "Clap your hands" : "Do Nothing"
todo
# => "Clap your hands"
todo = happy? and know_it? ? "Clap your hands" : "Do Nothing"
todo
# => true
and
has lower precedence, mostly we use it as a control-flow modifier such as if
:
next if widget = widgets.pop
becomes
widget = widgets.pop and next
For or
:
raise "Not ready!" unless ready_to_rock?
becomes
ready_to_rock? or raise "Not ready!"
I prefer to use if
but not and
, because if
is more intelligible, so I just ignore and
and or
.
Refer to "Using “and” and “or” in Ruby" for more information.
or
and||
. – Andrew Marshall