Ruby Details: clone and dup

Another post that’s mostly a reminder to self. 😉

Over at Know Ruby: clone and dup Aaron Lasseigne explained the differences between dup and clone.

However there’s another difference, and that’s the way the methods reproduce the methods an object can respond to. As is so often the case, a short session in a Ruby REPL (like irb or pry) helps to see things in action:

[1] pry(main)> o = Object.new
=> #<Object:0x00000102d298a0>
[2] pry(main)> def o.meth
[2] pry(main)* puts "meth called on object #{self.inspect}"
[2] pry(main)* end
=> :meth
[3] pry(main)> o.meth
meth called on object #<Object:0x00000102d298a0>
=> nil
[4] pry(main)> o_dupped = o.dup
=> #<Object:0x00000102101eb0>
[5] pry(main)> o_dupped.meth
NoMethodError: undefined method `meth' for #
from (pry):7:in `__pry__'
[6] pry(main)> o_cloned = o.clone
=> #<Object:0x00000102138168>
[7] pry(main)> o_cloned.meth
meth called on object #<Object:0x00000102138168>
=> nil

Note that both, clone and dup, return a new object, but only the one returned by clone also has the method defined for object o.
In other words: dup does not replicate an objects singleton methods.

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TextMate 1.5.10 … and Ruby 1.9.2

There’s a new version of Textmate available. Cool, thanks! However after installing … I couldn’t run Rake tasks anymore (the keyboard short cut to remember: Shift-Ctrl-R).

In ‘rake_mate.rb’ (line 49, /Applications/TextMate.app/Contents/SharedSupport/Bundles/Ruby.tmbundle/Support/RakeMate/rake_mate.rb). I inserted “.lines” to make it look like this:

tasks = [DEFAULT_TASK] + tasks.lines.grep(/^rake\s+(\S+)/) { |t| t.split[1] }

Additionally I had to ‘re-copy’ the plist.bundle as described on the rvm site.
Now everything works fine again.

Addendum: As mentioned in the rvm guide to using TextMate, I had to (re) move TextMate’s own Builder.rb out of the way:

cd /Applications/TextMate.app/Contents/SharedSupport/Support/lib/ ; mv Builder.rb Builder.rb.backup

Ruby, Sequel and Trees

While working on some tree structure a couple of unit tests failed, when creating some form of summary of said tree structure. First of all here’s a condensed form of the code:

require 'sequel'

DB = Sequel.sqlite
DB.create_table :items do
  primary_key :id
  String :name
  String :foo, :default => 'NOT SET'
  Integer :item_id
end

class Item < Sequel::Model
  one_to_many :items
  def summary
    if items.empty?
      return [ { self.name => self.foo } ]
    else
      items.inject( [] ){ | r, sub_res | r << sub_res.summary }
    end
  end
end

r1 = Item.create :name => 'R1'
r2 = Item.create :name => 'R2'

r1.add_item r2
r2.foo = 'Ding'
#r2.save

[ r1, r2 ].each{ |i|
  puts "Item    : #{ i.id }"
  puts "Direct Foo: #{ i.foo.inspect }"
  puts "Summary   : #{ i.summary.inspect }"
  puts
}

Notice, that I’ve commented out saving r2. The output is:

Item    : 1
Direct Foo: "NOT SET"
Summary   : [[{"R2"=>"NOT SET"}]]

Item    : 2
Direct Foo: "Ding"
Summary   : [{"R2"=>"Ding"}]

What I didn’t expect – and why the unit tests failed – is the ‘NOT SET’ in the r1 summary.

One way to end up with what I originally expected is to save r2. Another way is to set r2.foo before adding r1 to r1:

r2.foo = 'Ding'
r1.add_item r2

How ever I’m still not sure whether this is intended behaviour and why it should behave like this. (If it is, I’d like to know why.)
What do you think?