Difference between “and” and && in Ruby?

问题:

What is the difference between the && and and operators in Ruby?

回答1:

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 want to avoid and always

回答2:

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.

回答3:

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!

回答4:

|| 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/ .

回答5:

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, eg the assignment operator.

eg

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

回答6:

and has lower precedence, mostly we use it as 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.

Reference To

Using “and” and “or” in Ruby

回答7:

I don\'t know if this is Ruby intention or if this is a bug but try this code below. This code was run on Ruby version 2.5.1 and was on a Linux system.

puts 1 > -1 and 257 < 256
# => false

puts 1 > -1 && 257 < 256
# => true