Prevent side effects in Ruby

Question

a = [1,2,3,4]
b = a << 5
a == [1,2,3,4] # returns false

How to assign b to a with 5 appended to the end without modifying a itself?

score 9 · Answer 1 · answered Jul 14 '13 at 10:18

9

Just sum two arrays:

a = [1,2,3,4]
b = a + [5]

# b == [1, 2, 3, 4, 5]
# a == [1, 2, 3, 4]

answered Jul 14 '13 at 10:18

Yevgeniy Anfilofyev

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score 6 · Accepted Answer · answered Jul 14 '13 at 10:16

6

Ruby variables hold references to objects and the = operator copies the references.

It seems you wish to clone a:

irb(main):001:0> a = [1,2,3,4]
=> [1, 2, 3, 4]
irb(main):002:0> b = a.clone << 5
=> [1, 2, 3, 4, 5]
irb(main):003:0> a
=> [1, 2, 3, 4]
irb(main):004:0> b
=> [1, 2, 3, 4, 5]

answered Jul 14 '13 at 10:16

johnsyweb

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4

Or maybe [`dup`](http://www.ruby-doc.org/core-2.0/Object.html#method-i-dup), depending on what the OP wants. See also [What's the difference between Ruby's `dup` and `clone` methods?](http://stackoverflow.com/questions/10183370/whats-the-differences-between-ruby-dup-and-clone-method) – Andrew Marshall Jul 14 '13 at 16:26

score 5 · Answer 3 · answered Jul 14 '13 at 10:33

5

I usually do it this way:

b = [*a, 5]

answered Jul 14 '13 at 10:33

sawa

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3

Or more simply: `b = *a, 5` – Denis de Bernardy Jul 14 '13 at 17:34

Prevent side effects in Ruby

3 Answers3