Ruby - Return default value if variable is not present

Question

I often encounter the following case: I want to set a variable unless it is present. Of course this can be easily done by doing so:

var1 = ""
var1 = "dhiughr" unless var1.present?

If it was nil this could be done with a simple ||= operator, but since an empty string is not nil it won't work. I have tried reading on Ruby's or operator, which theoretically should work:

var1 = "" or "dhiughr"

but it doesn't. I expect the second string (right from the operator) to be chosen when the first isn't present?

What am I doing wrong?

Why in your opinion "or operator theoretically should work"? — Marek Lipka
– Marek Lipka, Commented Feb 18, 2014 at 12:29

Marek Lipka · Accepted Answer · 2014-02-18 12:44:31Z

8

You can do it this way, using Object#presence method (which comes as extension from active_support library):

var1 = var1.presence || 'dhiughr'

It works as you expect:

var1 = ''
var1 = var1.presence || 'dhiughr'
var1
# => "dhiughr"
var1 = 'foo'
var1 = var1.presence || 'dhiughr'
var1
# => "foo"

edited Feb 18, 2014 at 12:44

answered Feb 18, 2014 at 12:30

Marek Lipka

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3 Comments

scaryguy Over a year ago

Why wouldn't he use just ||= ?

Marek Lipka Over a year ago

@scaryguy read the question carefully and you'll get the answer.

scaryguy Over a year ago

I have no idea. I got 2 down votes for my answer and I deleted it.. People doesn't like others talking about their own vote status I guess.

Danil Speransky · Accepted Answer · 2014-02-18 12:33:27Z

1

In ruby empty string is truthy value. See What's truthy and falsey in Ruby?

Ruby:

var1 = ''
var1 = var1.to_s == '' ? 'dhiughr' : var1

With rails:

var1 = ''
var1 = var1.blank? ? 'dhiughr' : var1

edited Feb 18, 2014 at 12:33

answered Feb 18, 2014 at 12:27

Danil Speransky

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