What is wrong with the "not" operator ? 1

[mikrom]

Now, I'm learning Ruby and I don't understand the difference between the logical negation operators ! and not.

If I try this assignment with the ! operator

irb(main):001:0> x = true
=> true
irb(main):002:0> t = !x
=> false

then it works, but this similar thing with not doesn' work

irb(main):001:0> x = true
=> true
irb(main):002:0> t = not x
SyntaxError: compile error
(irb):2: syntax error, unexpected kNOT
t = not x
       ^
        from (irb):2
irb(main):003:0> t = not(x)
SyntaxError: compile error
(irb):3: syntax error, unexpected kNOT
t = not(x)
       ^
        from (irb):3

Why I get the error unexpected kNOT ???

However using not in logical condition (without assignment) works good

irb(main):001:0> something = false
=> false
irb(main):002:0> if not(something)
irb(main):003:1>   puts "It is False"
irb(main):004:1> else
irb(main):005:1*   puts "It is True"
irb(main):006:1> end
It is False
=> nil

What is the difference between the operators ! and not? Who can explain this strange behaviour of the operator not?

 

[feherke]

Hi

What is the difference between the operators ! and not?

[tt]![/tt] is a method and [tt]not[/tt] is an operator. At least according to this : Ruby Operator Precedence.

But your problem is just operator precedence :

irb(main):001:0> x = true
=> true
irb(main):002:0> t = [red]([/red]not x[red])[/red]
=> false

Feherke.

http://rootshell.be/~feherke/

 

[mikrom]

Thank you very much!

Did you mean that the precedence of the operator not is lower then the assignment =,
therefore we need to set it in parentheses?

 

[feherke]

Hi

Yepp. Apparently that is the situation. I would say, that operator precedence does not really match the POLS.

However, it has some logic if you used to put assignment for example in [tt]if[/tt] condition :

[b]if[/b] not result=myfairfunction : raise [i]'Gone bad'[/i] [b]end[/b]

process result

Feherke.

http://rootshell.be/~feherke/