Detect a Dimmension object without .typename

tbd

my mistake, i was wrong. if left side is false the right side doesn't get evaluated

Jim

if left side is false the right side doesn't get evaluated

This is my understanding also, but watch because the and operator is not the same as &&. I don't think and will shortcut.

thomthom

@jim said:

but watch because the and operator is not the same as &&. I don't think and will shortcut.

I did two more tests for this:


def test3
	if always_return_false and always_return_false
		#...
	end
end

def test4
	if always_return_true and always_return_true
		#...
	end
end

Results:


>> test3
call always_return_false
nil
>> test4
call always_return_true
call always_return_true
nil

thomthom

Found what the difference between and and && is:

@unknownuser said:

The binary "and" operator will return the logical conjunction of its two operands. It is the same as "&&" but with a lower precedence

AdamB

@thomthom said:

Found what the difference between and and && is:

@unknownuser said:

The binary "and" operator will return the logical conjunction of its two operands. It is the same as "&&" but with a lower precedence

Well that explains something that I've been bitten by a few times..

mask = mask or object.getmask

assigns mask to itself and ors with the results of object.getmask()!!

I end up having to do:

mask = (mask or object.getmask)

What kind of madman would introduce such an operator?

Actually the one that beats all for sheer insanity is ruby.h #define-ing fopen() to be something completely different calling some Ruby thing. What the!, Argggh...

I've got some harsh language for Mr.Ruby when/if I meet him.

Adam

thomthom

I think I've always used && and || so I've avoided such problems. But I have had unexpected behaviour when I used not instead of !. I used not some times simply because I thought it was the same thing - but not would read better.

Looking at the table of Operator Precedence I can see how it all fits together now. http://www.techotopia.com/index.php/Ruby_Operator_Precedence

AdamB

Sure, it lists them out.

But I see absolutely no compelling reason to have "Logical AND" differing from "Logical composition" wrt precedence.

What is the 'use case' for the 2 forms? Does anyone know?

Adam

tbd

@adamb said:

What is the 'use case' for the 2 forms? Does anyone know?

maybe to play jokes like this :


myvar = true and false
=> false
myvar
=> true

RickW

@adamb said:

I end up having to do:

mask = (mask or object.getmask)

But now you know you can use

mask = mask || object.getmask

It saves typing the parentheses... (FWIW)

thomthom

Saves you typing even more if you type mask ||= object.getmask