add element to ruby array return new array

Question

I would like to add an element to an array but without actually changing that array and instead it returning a new one. In other words, I want to avoid:

arr = [1,2]
arr << 3

Which would return:

[1,2,3]

Changing arr itself. How can I avoid this and create a new array?

Sergio Tulentsev · Accepted Answer · 2012-01-31 00:13:35Z

57

You can easily add two arrays in Ruby with plus operator. So, just make an array out of your element.

arr = [1, 2]
puts arr + [3]
# => [1, 2, 3]
puts arr
# => [1, 2]

answered Jan 31, 2012 at 0:13

Sergio Tulentsev

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2 Comments

gitb Over a year ago

Why is there no way in ruby to add an item to an array with affecting the original array?

rodamn Over a year ago

@gitb The array#+ method does this; it creates a new array from the left-hand side and the right-hand side of the plus operator and returns the new array, leaving both operands unmodified.

kazuwombat · Accepted Answer · 2016-10-19 13:29:46Z

16

it also works by extending arr using * operator

arr = [1,2]
puts [*arr, 3]
=> [1, 2, 3]

answered Oct 19, 2016 at 13:29

kazuwombat

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1 Comment

Juan José Ramírez Over a year ago

For those coming from JS or familiarized with it, this syntax is equivalent to the spread operator: ` const arr = [1,2]; console.log([...arr, 3] => [1, 2, 3] `

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