Best ruby idiom for "nil or zero"

Question

I am looking for a concise way to check a value to see if it is nil or zero. Currently I am doing something like:

if (!val || val == 0)
  # Is nil or zero
end

But this seems very clumsy.

Answer 1

I believe your code is incorrect; it will in fact test for three values: nil, false, and zero. This is because the !val expression is true for all values that are false, which in Ruby is nil and false.

The best I can come up with right now is

if val == nil || val == 0
  # do stuff
end

Which of course is not very clever, but (very) clear.

Answer 2

First off I think that's about the most concise way you can check for that particular condition.

Second, to me this is a code smell that indicates a potential flaw in your design. Generally nil and zero shouldn't mean the same thing. If possible you should try to eliminate the possibility of val being nil before you hit this code, either by checking that at the beginning of the method or some other mechanism.

You might have a perfectly legitimate reason to do this in which case I think your code is good, but I'd at least consider trying to get rid of the nil check if possible.

Answer 3

You can use the Object.nil? to test for nil specifically (and not get caught up between false and nil). You can monkey-patch a method into Object as well.

class Object
   def nil_or_zero?
     return (self.nil? or self == 0)
   end
end

my_object = MyClass.new
my_object.nil_or_zero?
==> false

This is not recommended as changes to Object are difficult for coworkers to trace, and may make your code unpredictable to others.

Answer 4

Rails does this via attribute query methods, where in addition to false and nil, 0 and "" also evaluate to false.

if (model.attribute?) # => false if attribute is 0 and model is an ActiveRecord::Base derivation

However it has its share of detractors. http://www.joegrossberg.com/archives/002995.html

Answer 5

Objects have a nil? method. See api here.

if (val.nil? or val == 0)
  [do something]
end

Or, for just one instruction:

[do something] if (val.nil? or val == 0)

Answer 6

I deal with this by defining an "is?" method, which I can then implement differently on various classes. So for Array, "is?" means "size>0"; for Fixnum it means "self != 0"; for String it means "self != ''". NilClass, of course, defines "is?" as just returning nil.

Answer 7

To be as idiomatic as possible, I'd suggest this.

if val.nil? or val == 0
    # Do something
end

Because:

• It uses the nil? method.
• It uses the "or" operator, which is preferable to ||.
• It doesn't use parentheses, which are not necessary in this case. Parentheses should only be used when they serve some purpose, such as overriding the precedence of certain operators.

Answer 8

val ||= 0
if val == 0
# do something here
end

Answer 9

If you really like method names with question marks at the end:

if val.nil? || val.zero?
  # do stuff
end

Your solution is fine, as are a few of the other solutions.

Ruby can make you search for a pretty way to do everything, if you're not careful.

Answer 10

I've just removed my previous answer. I misunderstood you and advised to use #blank? method.

Either way, I would extend Object class and create a method for this purpose.

Answer 11

You can use case if you like:

 case val with nil, 0
      # do stuff
 end

Then you can use anything that works with ===, which is nice sometimes. Or do something like this:

not_valid = nil, 0
case val1 with *not_valid
      # do stuff
 end
 #do other stuff
 case val2 with *not_valid, false    #Test for values that is nil, 0 or false
      # do other other stuff
 end

It's not exactly good OOP, but it's very flexible and it works. My ifs usually end up as cases anyway.

Of course Enum.any?/Enum.include? kind of works too ... if you like to get really cryptic:

if [0, nil].include? val
    #do stuff
end

The right thing to do is of course to define a method or function. Or, if you have to do the same thing with many values, use a combination of those nice iterators.

Answer 12

Another solution:

if val.to_i == 0
  # do stuff
end

Answer 13

nil.to_i returns zero, so I often do this:

val.to_i.zero?

However, you will get an exception if val is ever an object that does not respond_to #to_i.

Answer 14

I really like Rails blank? method for that kind of things, but it won't return true for 0. So you can add your method:

def nil_zero? 
  if respond_to?(:zero?) 
    zero? 
  else 
    !self 
  end 
end 

And it will check if some value is nil or 0:

nil.nil_zero?
=> true
0.nil_zero?
=> true
10.nil_zero?
=> false

if val.nil_zero?
  #...
end

Answer 15

Although to_i doesn't work, to_f does:

if val.to_f.zero?
# do something there
end