Difference between "and" and && in Ruby?
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 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!
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
.