[ruby-core:82593] [Ruby trunk Bug#13855] Hash#compact! returns nil if the hash is empty

Issue #13855 has been updated by shevegen (Robert A. Heiler).


Hmm.

I had a look at class String and class Array what they do.

First Array:

    array = [1,2,3] # => [1, 2, 3]
    array.compact!  # => nil

Next class String - it has no .compact but perhaps we can use
.delete! which may be somewhat similar:

    string = 'abc' # => "abc"
    string.delete! 'd' # => nil

So I assume that the nil returned there may be consistent behaviour. Probably
by nature of the assumption of what is returned, modification in place on
the same object, or a modification what would return a new object.

However had I do agree that, either way, the documentation could be more explicit.

No harm in mentioning that the hash.compact! variant will return nil, which is
what it is presently doing.

I do however had also agree that the behaviour may be a bit unexpected... so perhaps
the documentation can be fixed either way and then we can ask whether the behaviour
is the way it should be - but I actually assume that it may be just a documentation
problem.

----------------------------------------
Bug #13855: Hash#compact! returns nil if the hash is empty
https://bugs.ruby-lang.org/issues/13855#change-66414

* Author: elandesign (Paul Smith)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-darwin16]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
This behaviour feels like a bug to me.

From the documentation (with my emphasis):

> compact! → hsh
> Removes all nil values from the hash. **Returns the hash**.

However if the hash contains no keys, the method returns nil.

~~~
irb(main):001:0> {}.compact!
=> nil

# For Comparison
irb(main):002:0> { foo: nil }.compact!
=> {}
irb(main):003:0> {}.compact
=> {}
irb(main):004:0> { foo: nil }.compact
=> {}
~~~



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