Issue #14641 has been updated by hartator (Julien Khaleghy).


jeremyevans0 (Jeremy Evans) wrote:
> The array itself is not modified, you are mutating elements of the current array during iteration (as String#<< mutates the receiver), then returning a new array with the mutated elements (since String#<< returns the receiver).  If you don't want to mutate the elements, use String#+:
> 
> ~~~ ruby
> irb(main):001:0> a = ['a', 'b']
> => ["a", "b"]
> irb(main):002:0> a.map{|e| e + 'c'}
> => ["ac", "bc"]
> irb(main):003:0> a
> => ["a", "b"]
> irb(main):004:0> a.object_id
> => 11790377160340
> irb(main):005:0> a.map{|e| e << 'c'}.object_id
> => 11788696580840
> ~~~

It was my bad. Thanks for the explanation.


----------------------------------------
Bug #14641: Shouldn't Array#map not modify its array?
https://bugs.ruby-lang.org/issues/14641#change-71319

* Author: hartator (Julien Khaleghy)
* Status: Rejected
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 2.5.0 and 2.4.2
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
Hi, 

Thanks for the awesome work you guys have been doing on Ruby for all this years.

I might be missing something obvious, but I thought Array#map doesn't modify the array it's called on?

Ie.

~~~ ruby
ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-linux]
    a = ['a','b'] 
..    
=> ["a", "b"]
    a.map{|e| e << 'c'} 
=> ["ac", "bc"]
    a.map{|e| e << 'c'} 
=> ["acc", "bcc"]
    a.map{|e| e << 'c'} 
=> ["accc", "bccc"]
    a.map{|e| e << 'c'} 
=> ["acccc", "bcccc"]
   a
=> ["acccc", "bcccc"]
~~~

Expected `a` to be still ["a", "b"].

Same in Ruby 2.4 ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-darwin16]

~~~ ruby
irb(main):003:0*  a = ['a','b']
=> ["a", "b"]
irb(main):004:0>  a.map{|e| e << 'c'} 
=> ["ac", "bc"]
irb(main):005:0>  a.map{|e| e << 'c'} 
=> ["acc", "bcc"]
irb(main):006:0>  a.map{|e| e << 'c'} 
=> ["accc", "bccc"]
irb(main):007:0>  a.map{|e| e << 'c'} 
=> ["acccc", "bcccc"]
irb(main):008:0>  a 
=> ["acccc", "bcccc"]
~~~

Thanks for you guys time.




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