CODEWITHSUNDEEP
ruby
JP Silvashy
JP Silvashy

Reputation: 48535

Ruby: toggle a boolean inline?

How can I get the opposite of a boolean in Ruby (I know that it is converted to 0/1) using a method inline?

say I have the given instance:

class Vote

  def return_opposite
    self.value
  end

end

Which obviously doesn't do anything, but I can't seem to find a method that is simple and short something like opposite() or the like. Does something like this exist and I'm just not looking at the right place in the docs? If one doesn't exist is there a really short ternary that would toggle it from 1 => 0 or 0 => 1?

Upvotes: 14

Views: 28140

Answers (9)

Neka
Neka

Reputation: 26

I think that using a ternary can be interesting :

check = false
check == true ? check = false : check = true

Upvotes: 0

Christopher Oezbek
Christopher Oezbek

Reputation: 26453

Edit: See comment by @philomory below.

I believe this is basically an oversight in the boolean classes (TrueClass and FalseClass) in Ruby.

You can negate any object:

nil.! => true
false.! => true
true.! => false
0.! => false
1.! => false
a.! => false (all other objects)

But you cannot in-place negate the boolean objects:

a.!! => does not compile

I guess this would call for trouble with the compiler's grammar.

The best you can do, is thus:

a = a.!

Upvotes: 5

Dejan Stankovic
Dejan Stankovic

Reputation: 101

You can use XOR operator (exclusive or)

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

Upvotes: 8

DigitalRoss
DigitalRoss

Reputation: 146151

Boolean expressions are not 0 or 1 in Ruby, actually, 0 is not false

If n is numeric we are swapping 0 and 1...

n == 0 ? 1 : 0 # or...
1 - n          # or...
[1, 0][n]      # or maybe [1, 0][n & 1] # or...
class Integer; def oh_1; self==0 ? 1:0; end; end; p [12.oh_1, 0.oh_1, 1.oh_1] # or...
n.succ % 2     # or...
n ^= 1

If b already makes sense as a Ruby true or false conditional, it's going to be hard to beat:

!b

These examples differ in how they treat out-of-range input...

Upvotes: 22

Peak Sornpaisarn
Peak Sornpaisarn

Reputation: 975

In order to toggle a boolean data in rails you can do this vote.toggle!(:boolean)

Upvotes: 2

Rodrigo Zurek
Rodrigo Zurek

Reputation: 4575

I like to use this 

@object.boolean = [email protected]

Upvotes: 26

Sean M
Sean M

Reputation: 2030

In a Rails app, I use this method to toggle a post between paused and active, so ! (not) is my preferred method.

def toggle
  @post = Post.find(params[:id])

  @post.update_attributes paused: [email protected]?

  msg = @post.paused? ? 'The post is now paused.' : 'The post is now active.' 

  redirect_to :back, notice: msg
end

Upvotes: 0

pierrotlefou
pierrotlefou

Reputation: 40761

If you want to toggle boolean (that is false and true) , that would be as simple as just use ! as others has stated.

If you want to toggle between 0 and 1 , I can only think of something naive as below :)

def opposite
     op = {0=>1,1=>0}
     op[self.value]
end

Upvotes: 1

Tyler
Tyler

Reputation: 22126

If you just want to access the opposite of the value, use ! as some people have said in the comments. If you want to actually change the value, that would be bool_value = !bool_value. Unless I've misunderstood your question. Which is quite possible.

Upvotes: 3

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