[ruby-core:70719] [Ruby trunk - Bug #11520] Inconsistent behavior in Array#compact!

Issue #11520 has been updated by D.E. Akers.


This behavior is consistent with many other "bang methods" which return `nil` if they might have mutated the receiver but didn't:

``` ruby
[
  'foo'.downcase!,
  'BAR'.upcase!,
  'Baz'.capitalize!,

  'foo'.strip!,
  'bar'.lstrip!,
  'baz'.rstrip!,

  'foo'.sub!(/\d/, 'x'),
  'bar'.gsub!(/\d/, 'x'),
  'abc'.tr!('def', 'ghi'),

  [1,2,3].compact!,
  [1,2,3].flatten!,
  [1,2,3].uniq!
].any? # => false
```

This idiom is a Good Thing because it provides you with greater information density than if these methods simply returned the mutated receiver, since that's something to which you already have a reference. In the common enough case that you want to know whether something changed, you can simply use the return value rather than storing a copy of the object and comparing it before and after (potential) mutation.

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Bug #11520: Inconsistent behavior in Array#compact!
https://bugs.ruby-lang.org/issues/11520#change-54104

* Author: Hal Brodigan
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-linux]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
I noticed that `Array#compact!` sometimes returns `self` and other times `nil`. This behavior was a bit confusing.

    [].compact!
    # => nil
    
    [1].compact!
    # => nil
    
    [nil].compact!
    # => []
    
    [1, nil].compact!
    # => [1]

I would prefer that `Array#compact!` either always returns `nil`, or always returns `self`.



-- 
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