Issue #6087 has been updated by ko1 (Koichi Sasada). Eregon (Benoit Daloze) wrote in #note-14: > Much like all Enumerable methods return `Array` and (of course) do not copy instance variables, I think Array methods should do the same. +1 ---------------------------------------- Bug #6087: How should inherited methods deal with return values of their own subclass? https://bugs.ruby-lang.org/issues/6087#change-85409 * Author: marcandre (Marc-Andre Lafortune) * Status: Assigned * Priority: Normal * Assignee: matz (Yukihiro Matsumoto) * Target version: 3.0 * ruby -v: trunk ---------------------------------------- Just noticed that we still don't have a consistent way to handle return values: ```ruby class A < Array end a = A.new a.flatten.class # => A a.rotate.class # => Array (a * 2).class # => A (a + a).class # => Array ``` Some methods are even inconsistent depending on their arguments: ```ruby a.slice!(0, 1).class # => A a.slice!(0..0).class # => A a.slice!(0, 0).class # => Array a.slice!(1, 0).class # => Array a.slice!(1..0).class # => Array ``` Finally, there is currently no constructor nor hook called when making these new copies, so they are never properly constructed. Imagine this simplified class that relies on `@foo` holding a hash: ```ruby class A < Array def initialize(*args) super @foo = {} end def initialize_copy(orig) super @foo = @foo.dup end end a = A.new.flatten a.class # => A a.instance_variable_get(:@foo) # => nil, should never happen ``` I feel this violates object orientation. One solution is to always return the base class (`Array`/`String`/...). Another solution is to return the current subclass. To be object oriented, I feel we must do an actual `dup` of the object, including copying the instance variables, if any, and calling `initialize_copy`. Exceptions to this would be (1) explicit documentation, e.g. `Array#to_a`, or (2) methods inherited from a module (like `Enumerable` methods for `Array`). I'll be glad to fix these once there is a decision made on which way to go. -- https://bugs.ruby-lang.org/ Unsubscribe: <mailto:ruby-core-request / ruby-lang.org?subject=unsubscribe> <http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>