Bug #14251: String insert changing value of other string

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: 2.4.1p111 (2017-03-22 revision 58053) [x86_64-linux]
• Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN

[ricardovsilva (Ricardo Silva)]

foo = 'abc'
bar = foo
bar.insert(1, d)

puts foo 'adbc'
puts bar 'adbc'

The example above should only affect bar variable. It leads to an error by programmer.

A bypass that I found is to do:

foo = 'aaa'
bar = String.new foo
bar.insert(1, 'd')
puts foo #aaa
puts bar #adaa

[phluid61 (Matthew Kerwin)]

All Ruby variables are by-reference. To create a new object, use #dup

foo = 'abc'
bar = foo.dup
bar.insert(1, 'd')

[shevegen (Robert A. Heiler)]

Here is a blog entry that may be useful for ricardo:

https://aaronlasseigne.com/2014/07/20/know-ruby-clone-and-dup/

[ricardovsilva (Ricardo Silva)]

Because if you do

foo = 'aaa'
bar = foo
bar = bar + 'ccc' #here references of foo doesn't changes

puts foo #aaa
pubs bar #aaaccc

As I can see, ruby only for string as reference when I call string methods, like:

foo = 'abc'
bar = foo
bar.reverse!

puts foo #cba
puts bar #cba

Is that correct?

[dsferreira (Daniel Ferreira)]

I advise you to put this “issues” you find as questions in ruby talk before opening ruby core bugs.

In ruby objects are mutable and passed by reference.

When you do bar = bar + 'ccc'
you are allocating a new reference to bar object. The output object of the + operation.

Hope this helps.

Ruby talk is the right place for this things.

Welcome to ruby world!

[duerst (Martin Dürst)]

• Status changed from Open to Rejected

This behavior is expected. Except for purely functional programming languages, the difference between references and values is important to understand in every programming language, even if at first, it may be surprising.