[ruby-core:122384] [Ruby Bug#21392] Data classes do not allow overriding #inspect

2 Jun 2025

      Issue #21392 has been updated by austin (Austin Ziegler).

nobu (Nobuyoshi Nakada) wrote in #note-5:
...
austin (Austin Ziegler) wrote in #note-3:
...
You are correct (and I should have known better; I have unit tests proving this).
What unit tests?
In my feature branch where I'm converting to Data classes.
...
You can define `pretty_print` for IRB.
```ruby
    def pretty_print(q)
      q.text "CIELAB"
      q.breakable
      q.group 2, "[", "]" do
        q.text "%.4f%%" % l
        q.breakable
        q.text "%.4f" % a
        q.breakable
        q.text "%.4f" % b
      end
    end
```
This is the problem, of course, with having maintained something backwards compatible (Color is currently _nominally_ valid for 1.8) as long as I have. I wasn't aware that there was a new call for defining a pretty print, because IRB *used* to fall back to `inspect`. However, `Data` classes presumably define a pretty printer and overrides `#inspect` within IRB.

This is good to know, and I'll define a `pretty_print` method.

This can be closed.

----------------------------------------
Bug #21392: Data classes do not allow overriding #inspect
https://bugs.ruby-lang.org/issues/21392#change-113532

* Author: austin (Austin Ziegler)
* Status: Assigned
* Assignee: ima1zumi (Mari Imaizumi)
* ruby -v: 3.4.4
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
I'm preparing a new version of Color and I have decided to make all of the colour classes Data classes. However, it does not appear that `#inspect` can be overridden:

```ruby
module Color
  CIELAB = Data.define(:l, :a, :b) do
    def inspect
      "CIELAB [%.4f%% %.4f %.4f]" % [l, a, b]
    end
  end
end

p Color::CIELAB[1,2,3]
# Expected => CIELAB[1.000% 2.000 3.000]
# Actual #<data Color::CIELAB l=10, a=-125.0, b=20.5>
```

This feels like it should be permitted.

-- 
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