Issue #19786 has been updated by zverok (Victor Shepelev). It's a documentation bug :( The first implementations of `Data` had this feature, but then Matz said it is not necessary (it is considered a legacy in Struct anyway), and I removed the feature but probably forgot to adjust the comments. Already fixed in master: https://docs.ruby-lang.org/en/master/Data.html#method-c-define ---------------------------------------- Bug #19786: Data::define() does not work as documented https://bugs.ruby-lang.org/issues/19786#change-103994 * Author: thyresias (Thierry Lambert) * Status: Open * Priority: Normal * ruby -v: ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x64-mingw-ucrt] * Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN ---------------------------------------- Not sure if this is a bug or a feature. RDoc documentation for Data::define:
define(name, *symbols) → class define(*symbols) → class
Defines a new Data class. If the first argument is a string, the class is stored in Data::<name> constant.
```ruby M1 = Data.define('Measure', :amount, :unit) p M1 #=> M1 p M1.members #=> [:Measure, :amount, :unit] S1 = Struct.new('Measure', :amount, :unit) p S1 #=> Struct::Measure p S1.members #=> [:amount, :unit] ``` Unlike `Struct.new`, `Data.define` does not accept a name as first argument: it converts it to a symbol, and therefore a member. There is no trace of `Data::Measure` in the example above, while we do have `Struct::Measure`. -- https://bugs.ruby-lang.org/