[ruby-core:114946] [Ruby master Bug#19910] Set#delete_if behavior inconsistent with Array/Hash

Issue #19910 has been updated by stevegeek (Stephen Ierodiaconou).


I was just looking at this, and it seems like the behaviour used to be as you expected but changed in v2.1, https://github.com/ruby/ruby/commit/2849ee5d18360f26b55643a2643a1c597376865d 

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Bug #19910: Set#delete_if behavior inconsistent with Array/Hash
https://bugs.ruby-lang.org/issues/19910#change-104817

* Author: segiddins (Samuel Giddins)
* Status: Open
* Priority: Normal
* ruby -v: 3.2.2
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
Given the following script:

```ruby
#!/usr/bin/env ruby

require 'set'

def enum(collection)
  i = 0
  collection.delete_if do
    i += 1
    raise ArgumentError if i == 6
    i.odd?
  end
rescue ArgumentError
  return collection
end

pp enum([0, 1, 2, 3, 4, 5, 6, 7])
pp enum([0, 1, 2, 3, 4, 5, 6, 7].to_h { [_1, _1] })
pp enum([0, 1, 2, 3, 4, 5, 6, 7].to_set)
```

It results in:

```
[1, 3, 5, 6, 7]
{1=>1, 3=>3, 5=>5, 6=>6, 7=>7}
#<Set: {0, 1, 2, 3, 4, 5, 6, 7}>
```

As you can see, when an exception is raise inside `delete_if` on Hash/Array, the already-considered elements are still removed from the array. For `Set`, no elements are deleted (due to the implementation that builds up an intermediary list of elements to delete, then removes them from the underlying hash afterwards). It would be very helpful if `Set#delete_if` behaved consistently with other core collection types



-- 
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