Ruby's equivalent to C#'s ?? operator

c# ruby null-coalescing-operator

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Solution 1

The name of the operator is the null-coalescing operator. The original blog post I linked to that covered the differences in null coalescing between languages has been taken down. A newer comparison between C# and Ruby null coalescing can be found here.

In short, you can use ||, as in:

a_or_b = (a || b)

Solution 2

If you don't mind coalescing false, you can use the || operator:

a = b || c

If false can be a valid value, you can do:

a = b.nil? ? c : b

Where b is checked for nil, and if it is, a is assigned the value of c, and if not, b.

Solution 3

Be aware that Ruby has specific features for the usual null coalescing to [] or 0 or 0.0.

Instead of

x = y || [] # or...
x = y || 0

...you can (because NilClass implements them) just do...

x = y.to_a # => [] or ..
x = y.to_i # or .to_f, => 0

This makes certain common design patterns like:

(x || []).each do |y|

...look a bit nicer:

x.to_a.each do |y|

11,552

Author by

Shuo

Updated on June 14, 2022

Comments

Shuo about 2 years

Possible Duplicate:
C# ?? operator in Ruby?

Is there a Ruby operator that does the same thing as C#'s ?? operator?

The ?? operator returns the left-hand operand if it is not null, or else it returns the right operand.

from http://msdn.microsoft.com/en-us/library/ms173224.aspx
Shuo over 13 years

I tried a = b or c; puts a. Surprise, surprise, in my ruby 1.8.6, it prints the value of b. The reason is that or has lower precedence than =
Michael Kohl over 13 years

You'll also often see that as [*x].each do |y|.
orourkedd over 10 years

The link is now dead.
orourkedd over 10 years

or is not a boolean operator but a control flow operator in ruby: devblog.avdi.org/2010/08/02/using-and-and-or-in-ruby
Chris Pitman over 10 years

@orourkedd Thanks, I've reworked it a bit with a new link.
Kelvin almost 9 years

Unfortunately the 2nd snippet could have side-effects if b is a method (i.e. it's called twice).
Kelvin almost 9 years

This is actually a "falsy-coalescing operator".
Michael Lang almost 8 years

Link is a 404 again
olivervbk about 7 years

Its not the same thing. Does not work for boolean of other falsy values..
Mayuresh Srivastava over 6 years

according to this chrisarcand.com/… this is not null-coalescing operator. ||= is a conditional assignment operator. Is this article right?
Chris Pitman over 6 years

||= is different from ||
Chris Pitman about 4 years

@Cristik Thanks, updated the link hopefully for the last time ever