Keyword for exclusive or in ruby?

问题

Does Ruby have a plain-English keyword for exclusive or, like they have "and" and "or"? If not, is this because exclusive or doesn't allow evaluation short-cutting?

回答1:

Firstly, I don't think shortcircuiting can sensibly apply to XOR: whatever the value of the first operand, the second needs to be examined.

Secondly, and, &&, or and || use shortcircuiting in all cases; the only difference between the "word" and "symbol" versions is precedence. I believe that and and or are present to provide the same function as perl has in lines like

process_without_error or die

I think the reason for not having a xor named function is probably that there's no point in a low-precedence operator in this case and that it's already a confusing enough situation!

回答2:

No it doesn't, you can only use ^.

Don't know why there isn't particularly, may just be because it isn't as commonly used.

回答3:

I ran into an issue because the '^' operator acts bitwise on numbers,

true ^ 1
=> false

1 ^ true
TypeError: can't convert true into Integer
true ^ 1

so my workaround was:

( !!a ^ !!b ) where the double-bang coerces them into booleans.

!!1 ^ !!true
=> false

!!1 ^ !!false
=> true

回答4:

Try ^

true  ^ false #=> true
true  ^ true  #=> false
false ^ false #=> false

No plain english equivalent operator though.

回答5:

As an alternative to Matt Van Horn's double negation trick for using XOR on arbitrary types, you can chain another XOR test, starting with nil. i.e.:

!!foo ^ !!bar

is equivalent to

nil ^ foo ^ bar

This looks neater to my eye, and I suppose requires one less logical operation

回答6:

Any implementation of xor won't allow short circuiting. Both expressions need to be evaluated no matter what.

Ruby does provide the ^ operator, but this will choke on truthy values. I've implemented a function to handle the cases where I want an xor that behaves more like and and or:

def xor(a,b)
  (a and (not b)) or ((not a) and b)
end

Unlike ^, this function can be used in situations similar to the following:

xor("hello".match(/llo/), false) # => true
xor(nil, 1239)                   # => true
xor("cupcake", false)            # => false

回答7:

John's answer appears incorrect. In irb with 1.9.3, xor("cupcake", false) returns true, as you'd expect.

1.9.3-p429 :104 > def xor(a,b)
1.9.3-p429 :105?>     (a and (not b)) or ((not a) and b)
1.9.3-p429 :106?>   end
 => nil 
1.9.3-p429 :107 > xor(false, true)
 => true 
1.9.3-p429 :108 > xor("cupcake", false)
 => true

来源：https://stackoverflow.com/questions/585195/keyword-for-exclusive-or-in-ruby

标签

ruby

boolean

xor