[ruby-core:110663] [Ruby master Bug#19113] Inconsistency in retention of compare_by_identity flag in Hash methods

[ruby-core:110663] [Ruby master Bug#19113] Inconsistency in retention of compare_by_identity flag in Hash methods

[jeremyevans0 (Jeremy Evans)]

Issue #19113 has been reported by jeremyevans0 (Jeremy Evans).

----------------------------------------
Bug #19113: Inconsistency in retention of compare_by_identity flag in Hash methods
https://bugs.ruby-lang.org/issues/19113

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-11-07T17:29:28Z master 9001e53e68) [x86_64-openbsd7.2]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`Hash.[]` and `Hash.ruby2_keywords_hash` retain the compare_by_identity flag for non-empty hashes, but do not retain it for empty hashes:

```ruby
hs = [{}.compare_by_identity, {:a=>1}.compare_by_identity]
hs.map{|h| Hash[h].compare_by_identity?}
# => [false, true]
hs.map{|h| Hash.ruby2_keywords_hash(h).compare_by_identity?}
# => [false, true]
```

This inconsistency seems like a bug.

`Hash#compact` always drops the compare_by_identity flag, but it is documented as returning a copy of self, implying the compare_by_identity flag is kept (since #dup and #clone retain the flag).

```ruby
{}.compare_by_identity.compact.compare_by_identity?
# => false
```

I'm not sure whether is a bug, because it is consistent, but I think retaining the flag makes more sense.

I'll try to work on a fix for both of these issues tomorrow.



-- 
https://bugs.ruby-lang.org/

[ruby-core:110672] [Ruby master Bug#19113] Inconsistency in retention of compare_by_identity flag in Hash methods

[jeremyevans0 (Jeremy Evans)]

Issue #19113 has been updated by jeremyevans0 (Jeremy Evans).


I think the following behavior makes the most sense:

* `Hash.[]` should never retain the compare_by_identity flag.  It doesn't copy the default value/proc, so retaining the compare_by_identity flag does not make sense.
* `Hash.ruby2_keywords_hash` should always retain the compare_by_identity flag.  It copies the default value/proc, so retaining the compare_by_identity flag makes sense.
* `Hash#compact` should copy the default value/proc and retain the compare_by_identity flag.  It currently does neither.  However, the documentation says it returns a copy of the receiver, which implies the result should have the same default value/proc and compare_by_identity flag as the receiver.

I've submitted a pull request for these changes: https://github.com/ruby/ruby/pull/6702

----------------------------------------
Bug #19113: Inconsistency in retention of compare_by_identity flag in Hash methods
https://bugs.ruby-lang.org/issues/19113#change-100014

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-11-07T17:29:28Z master 9001e53e68) [x86_64-openbsd7.2]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`Hash.[]` and `Hash.ruby2_keywords_hash` retain the compare_by_identity flag for non-empty hashes, but do not retain it for empty hashes:

```ruby
hs = [{}.compare_by_identity, {:a=>1}.compare_by_identity]
hs.map{|h| Hash[h].compare_by_identity?}
# => [false, true]
hs.map{|h| Hash.ruby2_keywords_hash(h).compare_by_identity?}
# => [false, true]
```

This inconsistency seems like a bug.

`Hash#compact` always drops the compare_by_identity flag, but it is documented as returning a copy of self, implying the compare_by_identity flag is kept (since #dup and #clone retain the flag).

```ruby
{}.compare_by_identity.compact.compare_by_identity?
# => false
```

I'm not sure whether is a bug, because it is consistent, but I think retaining the flag makes more sense.

I'll try to work on a fix for both of these issues tomorrow.



-- 
https://bugs.ruby-lang.org/

[ruby-core:110759] [Ruby master Bug#19113] Inconsistency in retention of compare_by_identity flag in Hash methods

[ko1 (Koichi Sasada)]

Issue #19113 has been updated by ko1 (Koichi Sasada).


I think `Hash[]` remains all keys on the new Hash so `compare_by_identity` should be remained.


----------------------------------------
Bug #19113: Inconsistency in retention of compare_by_identity flag in Hash methods
https://bugs.ruby-lang.org/issues/19113#change-100099

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-11-07T17:29:28Z master 9001e53e68) [x86_64-openbsd7.2]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`Hash.[]` and `Hash.ruby2_keywords_hash` retain the compare_by_identity flag for non-empty hashes, but do not retain it for empty hashes:

```ruby
hs = [{}.compare_by_identity, {:a=>1}.compare_by_identity]
hs.map{|h| Hash[h].compare_by_identity?}
# => [false, true]
hs.map{|h| Hash.ruby2_keywords_hash(h).compare_by_identity?}
# => [false, true]
```

This inconsistency seems like a bug.

`Hash#compact` always drops the compare_by_identity flag, but it is documented as returning a copy of self, implying the compare_by_identity flag is kept (since #dup and #clone retain the flag).

```ruby
{}.compare_by_identity.compact.compare_by_identity?
# => false
```

I'm not sure whether is a bug, because it is consistent, but I think retaining the flag makes more sense.

I'll try to work on a fix for both of these issues tomorrow.



-- 
https://bugs.ruby-lang.org/

[ruby-core:110812] [Ruby master Bug#19113] Inconsistency in retention of compare_by_identity flag in Hash methods

[headius (Charles Nutter)]

Issue #19113 has been updated by headius (Charles Nutter).


jeremyevans0 (Jeremy Evans) wrote in #note-1:
> I think the following behavior makes the most sense:
> 
> * `Hash.[]` should never retain the compare_by_identity flag.  It doesn't copy the default value/proc, so retaining the compare_by_identity flag does not make sense.

I disagree. The contents of the other hash will have been populated using identity comparison rather than equality comparison. If that characteristic does not propagate to the new hash, any == keys will collide or else the set of keys will have to change. Is `Hash.[]` intended to make a copy, or a new hash populated with a subset of the original keys using non-identity, non-default semantics?

I agree with your other points.


----------------------------------------
Bug #19113: Inconsistency in retention of compare_by_identity flag in Hash methods
https://bugs.ruby-lang.org/issues/19113#change-100170

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-11-07T17:29:28Z master 9001e53e68) [x86_64-openbsd7.2]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`Hash.[]` and `Hash.ruby2_keywords_hash` retain the compare_by_identity flag for non-empty hashes, but do not retain it for empty hashes:

```ruby
hs = [{}.compare_by_identity, {:a=>1}.compare_by_identity]
hs.map{|h| Hash[h].compare_by_identity?}
# => [false, true]
hs.map{|h| Hash.ruby2_keywords_hash(h).compare_by_identity?}
# => [false, true]
```

This inconsistency seems like a bug.

`Hash#compact` always drops the compare_by_identity flag, but it is documented as returning a copy of self, implying the compare_by_identity flag is kept (since #dup and #clone retain the flag).

```ruby
{}.compare_by_identity.compact.compare_by_identity?
# => false
```

I'm not sure whether is a bug, because it is consistent, but I think retaining the flag makes more sense.

I'll try to work on a fix for both of these issues tomorrow.



-- 
https://bugs.ruby-lang.org/

[ruby-core:110813] [Ruby master Bug#19113] Inconsistency in retention of compare_by_identity flag in Hash methods

[headius (Charles Nutter)]

Issue #19113 has been updated by headius (Charles Nutter).


FWIW I ran into this while implementing Ruby 3.1 identhash semantics in JRuby, and then realized this is now one of the few "copy" paths that does not propagate identity comparison.

----------------------------------------
Bug #19113: Inconsistency in retention of compare_by_identity flag in Hash methods
https://bugs.ruby-lang.org/issues/19113#change-100171

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-11-07T17:29:28Z master 9001e53e68) [x86_64-openbsd7.2]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`Hash.[]` and `Hash.ruby2_keywords_hash` retain the compare_by_identity flag for non-empty hashes, but do not retain it for empty hashes:

```ruby
hs = [{}.compare_by_identity, {:a=>1}.compare_by_identity]
hs.map{|h| Hash[h].compare_by_identity?}
# => [false, true]
hs.map{|h| Hash.ruby2_keywords_hash(h).compare_by_identity?}
# => [false, true]
```

This inconsistency seems like a bug.

`Hash#compact` always drops the compare_by_identity flag, but it is documented as returning a copy of self, implying the compare_by_identity flag is kept (since #dup and #clone retain the flag).

```ruby
{}.compare_by_identity.compact.compare_by_identity?
# => false
```

I'm not sure whether is a bug, because it is consistent, but I think retaining the flag makes more sense.

I'll try to work on a fix for both of these issues tomorrow.



-- 
https://bugs.ruby-lang.org/

[ruby-core:110814] [Ruby master Bug#19113] Inconsistency in retention of compare_by_identity flag in Hash methods

[jeremyevans0 (Jeremy Evans)]

Issue #19113 has been updated by jeremyevans0 (Jeremy Evans).


headius (Charles Nutter) wrote in #note-3:
> jeremyevans0 (Jeremy Evans) wrote in #note-1:
> > I think the following behavior makes the most sense:
> > 
> > * `Hash.[]` should never retain the compare_by_identity flag.  It doesn't copy the default value/proc, so retaining the compare_by_identity flag does not make sense.
> 
> I disagree. The contents of the other hash will have been populated using identity comparison rather than equality comparison. If that characteristic does not propagate to the new hash, any == keys will collide or else the set of keys will have to change. Is `Hash.[]` intended to make a copy, or a new hash populated with a subset of the original keys using non-identity, non-default semantics?

It's explicitly documented as returning a new hash, not a copy: `Returns a new Hash object populated with the given objects`.

The fact that it doesn't copy the default value/proc indicates to me that the compare_by_identity flag should not be copied either.  However, I don't feel strongly regarding this.  We can make it so the compare_by_identity flag is always copied.  We do need to make some change, because the current behavior is inconsistent.

----------------------------------------
Bug #19113: Inconsistency in retention of compare_by_identity flag in Hash methods
https://bugs.ruby-lang.org/issues/19113#change-100172

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-11-07T17:29:28Z master 9001e53e68) [x86_64-openbsd7.2]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`Hash.[]` and `Hash.ruby2_keywords_hash` retain the compare_by_identity flag for non-empty hashes, but do not retain it for empty hashes:

```ruby
hs = [{}.compare_by_identity, {:a=>1}.compare_by_identity]
hs.map{|h| Hash[h].compare_by_identity?}
# => [false, true]
hs.map{|h| Hash.ruby2_keywords_hash(h).compare_by_identity?}
# => [false, true]
```

This inconsistency seems like a bug.

`Hash#compact` always drops the compare_by_identity flag, but it is documented as returning a copy of self, implying the compare_by_identity flag is kept (since #dup and #clone retain the flag).

```ruby
{}.compare_by_identity.compact.compare_by_identity?
# => false
```

I'm not sure whether is a bug, because it is consistent, but I think retaining the flag makes more sense.

I'll try to work on a fix for both of these issues tomorrow.



-- 
https://bugs.ruby-lang.org/

[ruby-core:110815] [Ruby master Bug#19113] Inconsistency in retention of compare_by_identity flag in Hash methods

[headius (Charles Nutter)]

Issue #19113 has been updated by headius (Charles Nutter).


Even though it's a "new Hash", it is supposed to be populated with "the given objects". If losing identity comparison means some keys don't get populated, I would consider that broken.

----------------------------------------
Bug #19113: Inconsistency in retention of compare_by_identity flag in Hash methods
https://bugs.ruby-lang.org/issues/19113#change-100173

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-11-07T17:29:28Z master 9001e53e68) [x86_64-openbsd7.2]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`Hash.[]` and `Hash.ruby2_keywords_hash` retain the compare_by_identity flag for non-empty hashes, but do not retain it for empty hashes:

```ruby
hs = [{}.compare_by_identity, {:a=>1}.compare_by_identity]
hs.map{|h| Hash[h].compare_by_identity?}
# => [false, true]
hs.map{|h| Hash.ruby2_keywords_hash(h).compare_by_identity?}
# => [false, true]
```

This inconsistency seems like a bug.

`Hash#compact` always drops the compare_by_identity flag, but it is documented as returning a copy of self, implying the compare_by_identity flag is kept (since #dup and #clone retain the flag).

```ruby
{}.compare_by_identity.compact.compare_by_identity?
# => false
```

I'm not sure whether is a bug, because it is consistent, but I think retaining the flag makes more sense.

I'll try to work on a fix for both of these issues tomorrow.



-- 
https://bugs.ruby-lang.org/

[ruby-core:110816] [Ruby master Bug#19113] Inconsistency in retention of compare_by_identity flag in Hash methods

[jeremyevans0 (Jeremy Evans)]

Issue #19113 has been updated by jeremyevans0 (Jeremy Evans).


headius (Charles Nutter) wrote in #note-6:
> Even though it's a "new Hash", it is supposed to be populated with "the given objects". If losing identity comparison means some keys don't get populated, I would consider that broken.

If you turn the hash into an array, you have the same `given objects`, but different results:

```ruby
h = {'a'=>1}.compare_by_identity
h['a'] = 2
Hash[h]      # {'a'=>1, 'a'=>2}.compare_by_identity
Hash[h.to_a] # {'a'=>2}
```

Not respecting the compare_by_identity flag (as my PR does) would make `Hash[h] == Hash[h.to_a]`.

I would say that `populated with the given objects` does not imply `resulting in the same set of keys.`  Also, `given objects` (not `given object`) implies it looks at the content of the hash, but not the hash object itself (hence why default value/proc is not copied).

Here's the pseudocode I would consider based on the documentation:

```ruby
# new hash
output_hash = {}
# populated with the given objects
input_hash_or_array.each do |k, v|
  output_hash[k] = v
end
output_hash
```

There are certainly valid arguments for both sides, so we'll have to see what @matz decides. 

----------------------------------------
Bug #19113: Inconsistency in retention of compare_by_identity flag in Hash methods
https://bugs.ruby-lang.org/issues/19113#change-100174

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-11-07T17:29:28Z master 9001e53e68) [x86_64-openbsd7.2]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`Hash.[]` and `Hash.ruby2_keywords_hash` retain the compare_by_identity flag for non-empty hashes, but do not retain it for empty hashes:

```ruby
hs = [{}.compare_by_identity, {:a=>1}.compare_by_identity]
hs.map{|h| Hash[h].compare_by_identity?}
# => [false, true]
hs.map{|h| Hash.ruby2_keywords_hash(h).compare_by_identity?}
# => [false, true]
```

This inconsistency seems like a bug.

`Hash#compact` always drops the compare_by_identity flag, but it is documented as returning a copy of self, implying the compare_by_identity flag is kept (since #dup and #clone retain the flag).

```ruby
{}.compare_by_identity.compact.compare_by_identity?
# => false
```

I'm not sure whether is a bug, because it is consistent, but I think retaining the flag makes more sense.

I'll try to work on a fix for both of these issues tomorrow.



-- 
https://bugs.ruby-lang.org/

[ruby-core:110817] [Ruby master Bug#19113] Inconsistency in retention of compare_by_identity flag in Hash methods

[Eregon (Benoit Daloze)]

Issue #19113 has been updated by Eregon (Benoit Daloze).


The way I see it, `Hash[*args]` converts args to a Hash, and args is only considered as key-value pairs. So if `args = [some_Hash]`, it's just one of the representation of key-value pairs but the behavior shouldn't be special with a Hash argument otherwise.
IOW I agree with Jeremy here. To copy a Hash there is `.dup`/`.clone`.

----------------------------------------
Bug #19113: Inconsistency in retention of compare_by_identity flag in Hash methods
https://bugs.ruby-lang.org/issues/19113#change-100175

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-11-07T17:29:28Z master 9001e53e68) [x86_64-openbsd7.2]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`Hash.[]` and `Hash.ruby2_keywords_hash` retain the compare_by_identity flag for non-empty hashes, but do not retain it for empty hashes:

```ruby
hs = [{}.compare_by_identity, {:a=>1}.compare_by_identity]
hs.map{|h| Hash[h].compare_by_identity?}
# => [false, true]
hs.map{|h| Hash.ruby2_keywords_hash(h).compare_by_identity?}
# => [false, true]
```

This inconsistency seems like a bug.

`Hash#compact` always drops the compare_by_identity flag, but it is documented as returning a copy of self, implying the compare_by_identity flag is kept (since #dup and #clone retain the flag).

```ruby
{}.compare_by_identity.compact.compare_by_identity?
# => false
```

I'm not sure whether is a bug, because it is consistent, but I think retaining the flag makes more sense.

I'll try to work on a fix for both of these issues tomorrow.



-- 
https://bugs.ruby-lang.org/

[ruby-core:111389] [Ruby master Bug#19113] Inconsistency in retention of compare_by_identity flag in Hash methods

[matz (Yukihiro Matsumoto) via ruby-core]

Issue #19113 has been updated by matz (Yukihiro Matsumoto).


I agree with @jeremyevans0 too.

Matz.


----------------------------------------
Bug #19113: Inconsistency in retention of compare_by_identity flag in Hash methods
https://bugs.ruby-lang.org/issues/19113#change-100764

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-11-07T17:29:28Z master 9001e53e68) [x86_64-openbsd7.2]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`Hash.[]` and `Hash.ruby2_keywords_hash` retain the compare_by_identity flag for non-empty hashes, but do not retain it for empty hashes:

```ruby
hs = [{}.compare_by_identity, {:a=>1}.compare_by_identity]
hs.map{|h| Hash[h].compare_by_identity?}
# => [false, true]
hs.map{|h| Hash.ruby2_keywords_hash(h).compare_by_identity?}
# => [false, true]
```

This inconsistency seems like a bug.

`Hash#compact` always drops the compare_by_identity flag, but it is documented as returning a copy of self, implying the compare_by_identity flag is kept (since #dup and #clone retain the flag).

```ruby
{}.compare_by_identity.compact.compare_by_identity?
# => false
```

I'm not sure whether is a bug, because it is consistent, but I think retaining the flag makes more sense.

I'll try to work on a fix for both of these issues tomorrow.



-- 
https://bugs.ruby-lang.org/
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