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Ruby: difference between || and ‘or’

Using Ruby

||

and

or 

are very common practices which makes it important to know the difference between the two as unfortunately I am not sure.

First of all my question is if the following assumption is correct:

EX1:

if @variable_1 || @variable_2 || @variable_3 
  do something 
else
  do nothing
end

EX2:

if @variable_1 or @variable_2 or @variable_3
  do something 
else
  do nothing
end

So in the first example if any variable is false then it will execute “do nothing”

However, for the second example all variables are checked and if one is true then it will execute “do something”.

In summary use “||” if you have a list of variables that need to be checked and if one of them returns false then a flag goes up. Use the second example with a list of variables where only one needs to be true in order to continue executing the desired code.

Are these assumptions correct?

Answer 1

or the second example all variables are checked and if one is true then it will execute “do something”.

This is false sentence.

As a result your assumptions are not correct.

Both or and || do the same thing.

The main difference is that or has lower precedence than ||. So you should pay attention to more complex evaluations:

# Simple cases are not confusing
false || true # true
false or true # true

# This is more complex
a = false || true # a=true
a = false or true # a=false

# Also similarly as 1 + 2*3 returns 7, the following returns true:
false or false||true # true
# BUT! THIS IS IMPORTANT!
a = false or false||true   # a=false
a = (false or false||true) # a=true

Here is a list of operators precedence.

So the real difference will be noticed if you use the expression that includes any of the following operators:

• .. ... – Range (inclusive and exclusive)
• ? : – Ternary if-then-else
• = %= { /= -= += |= &= >>= <<= *= &&= ||= **= – Assignment
• defined? – Check if specified symbol defined
• not – Logical negation
• and – Logical composition

there might be others too.

You can thing about the difference between those as different between + and *: ||==* and or=+. The same applies to and and not.

You should really pay attention to that.

Personally I prefer || operator as its semantics is well understood and avoid or.

While it ‘feels’ like or is more friendly in many cases (see my code sample), even in trivial ones, it is a source of bugs.