Feature #1880: Hash#flatten Doesn't Operate Recursively for Hash Values

• Status: Rejected
• Assignee: matz (Yukihiro Matsumoto)
• Target version: 2.0.0

[runpaint (Run Paint Run Run)]

=begin
Hash#flatten claims to flatten recursively if given an argument specifying the depth. This works as expected for Array values, but has no bearing on Hash values.

h = {orange: :orange, coconut: {inside: :white, outside: :brown}, grapes: {colour: [:red, :green]}}
h.flatten
=> [:orange, :orange, :coconut, {:inside=>:white, :outside=>:brown}, :grapes, {:colour=>[:red, :green]}]
h.flatten(20)
=> [:orange, :orange, :coconut, {:inside=>:white, :outside=>:brown}, :grapes, {:colour=>[:red, :green]}]

This seems peculiar. If the user has specified a depth he's explicitly stating the level of recursion to flatten; not how he wants Array values to be treated. IOW, I expected #flatten(depth) to call #flatten on Hash values as appropriate. This can be generalised to: call #flatten on values until the depth has been reached.
=end

[marcandre (Marc-Andre Lafortune)]

• Assignee set to matz (Yukihiro Matsumoto)
• Priority changed from 3 to Normal
• Target version set to 1.9.2

=begin
Moving this from 'bug' to 'feature request' as behavior corresponds to doc. Currently it converts to an array and (if given an argument) calls flatten on it. Array#flatten leaves hashes alone.

The question remaining: should there be a way to recursively flatten hashes, via Hash#flatten or otherwise?
=end

[mame (Yusuke Endoh)]

=begin
Hi,

Hash#flatten claims to flatten recursively if given an argument specifying the depth. This works as expected for Array values, but has no bearing on Hash values.

I wonder why recursive Hash#flatten is needed :-)
I can't imagine any use case.

--
Yusuke Endoh [e-mail]
=end

[znz (Kazuhiro NISHIYAMA)]

• Target version changed from 1.9.2 to 2.0.0

=begin

=end

[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Assigned

=begin

=end

[mame (Yusuke Endoh)]

• Status changed from Assigned to Rejected

I'm rejecting this feature ticket because no progress has been
made for a long time. See [ruby-core:42391].

I think flatten means an operation on Array, in Ruby.
"flatten" on Hash is also possible, but Hash#flatten is not for
that. I think we need:

• a use case
• another appropriate name
• detailed semantics (what does {a: {a: 1}}.flatten return?)

--
Yusuke Endoh [e-mail]