How can I avoid iterating over a nil array in Ruby?

Question

I want avoid iterating over a nil array.

My bad solution:

if nil!=myArr
    myArr.each { |item|
      p item;
    }
 end

score 29 · Answer 1 · edited May 23 '17 at 11:54

29

For a simple one-liner, you might also use unless myArr.nil?

myArr.each { |item| p item } unless myArr.nil?

Updating for Ruby >= 2.3.0:

If you are comfortable with a nil return rather than avoiding execution entirely, you can use the Safe navigation operator &.. Note though that this differs slightly. Whereas the unless version will skip execution entirely, the &. will execute but return nil.

myArr&.each { |item| p item }
# returns nil

edited May 23 '17 at 11:54

Community

1
1

answered Mar 26 '12 at 14:24

Michael Berkowski

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Using `nil?` is almost always extraneous unless you are specifically testing a value that could be the value `false`, not just false from a boolean perspective. – tadman Mar 26 '12 at 15:48
Use of & operator for ruby 2.3 is fantastic (myArr&.each { |item| p item }) – Simonini Feb 22 '17 at 11:24
Thanks for introducing & operator. It's fantastic! – Aboozar Rajabi Apr 19 '19 at 13:54

score 15 · Accepted Answer · answered Mar 26 '12 at 14:19

15

In ruby, only nil and false are considered as false.

if myArr
    myArr.each { |item|
      p item
    }
end

answered Mar 26 '12 at 14:19

xdazz

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You can also collapse this to `myArr and myArr.each ...` – tadman Mar 26 '12 at 15:47

score 13 · Answer 3 · answered Oct 14 '15 at 16:47

13

You can wrap the array value in Array().

Array(myArr).each { |item| p item }

As per the documentation, does this:

An array can also be created by using the Array() method, provided by Kernel, which tries to call to_ary, then to_a on its argument.

Basically, this will convert a nil value to []. Which would neither iterate, or throw an error. Fair warning, it will do the same to any value. Array("string") will create ["string"].

answered Oct 14 '15 at 16:47

Cereal

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@muistooshort GetSet's answer works only for Rails. This answer works for plain Ruby as well. – Wayne Conrad Oct 14 '15 at 17:04

score 3 · Answer 4 · answered Mar 26 '12 at 15:25

Simply checking for nil isn't always sufficient. Sometimes a variable you expect to be an array can be initialized as a non-array object when there is only one. It's not common, but proprietary services I've seen might give you a result of nil, "Name1", or ["Name1", "Name2", ...]. To reliably handle this range of input, I prefer to access my arrays like this:

Array.wrap(myArr).each { |item|
  p item
}

Array.wrap will convert nil to [], Object to [Object], and leave existing arrays alone. Also handy for not silently butchering your hashes if one gets passed in instead of an array. (Calling Array(myArr) will convert myArr into an array, which destroys hashes rather than wrapping them in arrays.

Plain ruby Array will also convert nil to [], Object to [Object], and leave existing arrays alone. You are right about Hashes. — shushugah, Feb 09 '19 at 17:10

score 2 · Answer 5 · answered Mar 26 '12 at 14:24

2

Alternatively, using andand

myArr.andand.each { | item| p item }

answered Mar 26 '12 at 14:24

markijbema

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score 1 · Answer 6 · answered Mar 26 '12 at 14:26

1

myArr ||= []

and then iterate. This will assign empty array to myArr only if it's nil.

answered Mar 26 '12 at 14:26

Sergey

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No, it won't. It will also assign if it is `false`. – Jörg W Mittag Mar 27 '12 at 13:43

How can I avoid iterating over a nil array in Ruby?

6 Answers6

Updating for Ruby >= 2.3.0: