Ruby: "&& Return" VS "And Return"

Ruby: && return vs and return

Check out the difference between and and &&. In the examples you give the method puts is called without parens around it's arguments and the difference in precedence changes how it is parsed.

In test 1 && has higher precedence than the method call. So what's actually happening is puts('hello' && return). Arguments are always evaluated before the methods they're called with -- so we first evaluate 'hello' && return. Since 'hello' is truthy the boolean does not short circuit and return is evaluated. When return we exit the method without doing anything else: so nothing is ever logged and the second line isn't run.

In test 2 and has a lower precedence than the method call. So what happens is puts('hello') and return. The puts method logs what is passed to it and then returns nil. nil is a falsey value so the and expression short circuits and the return expression is never evaluated. We just move to the second line where puts 'world' is run.

Can (a== 1 && a ==2 && a==3) ever evaluate to true?

If you take advantage of how == works, you could simply create an object with a custom toString (or valueOf) function that changes what it returns each time it is used such that it satisfies all three conditions.

const a = {  i: 1,  toString: function () {    return a.i++;  }}
if(a == 1 && a == 2 && a == 3) {  console.log('Hello World!');}

RSpec redirect_to and return vs. redirect_to && return

As per the Rails guide:

Make sure to use and return instead of && return because && return will not work due to the operator precedence in the Ruby Language.

If you prefer to use &&, enclose the arguments to render in parentheses:

redirect_to(root_path) && return

Ruby: how to combine puts and return inside if condition?

Because Ruby reads this line

print "Your number is: #{num}" && return if num > 10

like this

print("Your number is: #{num}" && return) if num > 10

That leads the method to return before it had the chance to print anything.

Adding a pair of parenthesis helps Ruby to resolve the desired order:

print("Your number is: #{num}") || return if num > 10

Why does Ruby expression with double ampersand using a return statement cause a syntax error

Side Note

It is worth noting that and and && are not equivalent.

and is a flow control operator while && is a Boolean operator. What is the difference?

One example of the differences, using and, you can assign values.

value = nil and value / 42

This would fail if you tried it as below

value = nil && value / 42

Original Question 1

Assuming I want to evaluate one-liners with a return statement (similar to a certain > commonly used shell/bash expression), would this be a recommended way to do it, or is there > a more recommended approach?

The way I have always seen this done in Ruby is this:

value if conditional

This will return the value if the conditional is met and nil otherwise. No need for the return statement if this is the last command in the function!

If you are using this for an early exit to a function, I prefer using an unless. For instance...

return unless arguments_are_valid

Original Question 2

foo method causes a syntax error. bar doesn't. Why?

It's a matter of operator precedence. See the example below showing how they are evaluated.

(true && return) false
(true) and (return false)

rails rubocop use && instead of and with render and return

Like a comment under your Post, indeed you don't need to return here.

However if you still want to use return and have it following RuboCop style, try wrapping render params with brackets.

render('errors/status_code', layout: 'errors/status_code', status: @error_code) && return

Difference between or and || in Ruby?

It's a matter of operator precedence.

|| has a higher precedence than or.

So, in between the two you have other operators including ternary (? :) and assignment (=) so which one you choose can affect the outcome of statements.

Here's a ruby operator precedence table.

See this question for another example using and/&&.

Also, be aware of some nasty things that could happen:

a = false || true  #=> true
a  #=> true

a = false or true  #=> true
a  #=> false

Both of the previous two statements evaluate to true, but the second sets a to false since = precedence is lower than || but higher than or.

is there a ruby one-line return if x ?

is there a ruby one-line “return if x” ?

Yes:

return value if condition

I love Ruby :-)

---

Related Topics