ruby-core

Issue #13797 has been updated by nobu (Nobuyoshi Nakada).

Description updated
Status changed from Open to Rejected

You share the same array instance as sub-arrays.

```ruby
                def initialize(totalSize)
                        @data_array = Array.new(totalSize,[])   
                end
```

Make different instances.

```ruby
@data_array = Array.new(totalSize) {[]}
```
or 

```ruby
@data_array = [[]] * totalSize
```


----------------------------------------
Bug #13797: Using .push on an 2d array class-instance variable causes the whole array to be overwritten with the .push value; is this a bug?
https://bugs.ruby-lang.org/issues/13797#change-66127

* Author: gggfx (James Pike)
* Status: Rejected
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.2.6p396 (2016-11-15 revision 56800) [x64-mingw32]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
I was building a class to hold results for analysis 'cells' in a model;  each 'cell' is a position in an array, with each result stored in a sub-array - this collates multiple results per cell which can then be iterated through later for model interactions.

I created this as a class (my data is addressed by time,x,y and z coordinates; my class writers and readers convert t-x-y-z into a position on a 1d array, this is faster than named instance variables).

When it comes to pushing the data into the instance array variable it causes *all* the slots of the array to be pushed with the value.

This is my first bug report and I'm newish to Ruby so I apologise if I've missed any key information.  I attach code with a test-example I wrote which demonstrates the behaviour in question.


## NORMAL CASE

```ruby
testArray = [[],[],[],[],[]]
testArrayShouldLookLike = [[result1],[],[],[],[]]
testArrayCanThenLookLike = [[result1, result2],[],[],[],[]]  etc.
```

## CLASS CASE

```ruby
def write(position, data)
    @testArray[position].push(data)
end

testArrayComesOutAs = [[result1],[result1],[result1],[result1],[result1]]
```

---Files--------------------------------
Class bug_JP.rb (1.13 KB)


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