Bug #19786: Data::define() does not work as documented

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x64-mingw-ucrt]
• Backport: 3.0: DONTNEED, 3.1: DONTNEED, 3.2: DONE

[thyresias (Thierry Lambert)]

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:: constant.

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.

[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

[thyresias (Thierry Lambert)]

zverok (Victor Shepelev) wrote in #note-1:

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

Thank you Victor for the update.
The behavior of Struct.new with a name is indeed a bit weird, so I was expecting this to be a feature rather than a bug, but I filed it since it was written in the bible documentation. ^_^

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed
• Backport changed from 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN to 3.0: DONTNEED, 3.1: DONTNEED, 3.2: REQUIRED

It was fixed at cada537040743cbe49aac6740816d648ca0d3fb6.
To be backported.

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 3.0: DONTNEED, 3.1: DONTNEED, 3.2: REQUIRED to 3.0: DONTNEED, 3.1: DONTNEED, 3.2: DONE

ruby_3_2 19a3466a1460924058ca16a259601bb753293d43 merged revision(s) cada537040743cbe49aac6740816d648ca0d3fb.