This tripped me up (again) today

Dan Rathbun

I'm using SU 15, which is supposed to have Ruby 2.0 and Dan notes that dclone is in 1.9, so I'm confused.

What I actually said was that the REXML library (beginning in Ruby 1.9,) modified the Array class, by adding the dclone method.

In order to use it, you must either precede it's use with:
require "rexml/document"
or use a refinement.

(1) Using the REXML library:
` require "rexml/document"

true
a = []
[]
a.respond_to?(:dclone)
true`

(2) Refinement module:

<span class="syntaxdefault"><br />module&nbsp;August<br />&nbsp;&nbsp;module&nbsp;DeepCopy<br /><br />&nbsp;&nbsp;&nbsp;&nbsp;refine&nbsp;</span><span class="syntaxkeyword">Array&nbsp;do<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="syntaxdefault">def&nbsp;dclone<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;klone&nbsp;</span><span class="syntaxkeyword">=&nbsp;</span><span class="syntaxdefault">self</span><span class="syntaxkeyword">.clone<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="syntaxdefault">klone</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">clear<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;self</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">each</span><span class="syntaxkeyword">{|</span><span class="syntaxdefault">v</span><span class="syntaxkeyword">|&nbsp;</span><span class="syntaxdefault">klone&nbsp;</span><span class="syntaxkeyword"><<&nbsp;</span><span class="syntaxdefault">v</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">dclone</span><span class="syntaxkeyword">}<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="syntaxdefault">klone<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;end<br />&nbsp;&nbsp;&nbsp;&nbsp;end&nbsp;</span><span class="syntaxcomment">#&nbsp;class&nbsp;Array<br /><br />&nbsp;&nbsp;</span><span class="syntaxdefault">end&nbsp;</span><span class="syntaxcomment">#&nbsp;refinement&nbsp;module&nbsp;DeepCopy<br /></span><span class="syntaxdefault">end&nbsp;</span><span class="syntaxcomment">#&nbsp;Author's&nbsp;namespace<br /><br /><br /></span><span class="syntaxdefault">using&nbsp;August</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">DeepCopy<br /><br />module&nbsp;August<br />&nbsp;&nbsp;module&nbsp;SomePlugin<br />&nbsp;&nbsp;&nbsp;&nbsp;<br />&nbsp;&nbsp;&nbsp;&nbsp;a&nbsp;</span><span class="syntaxkeyword">=&nbsp;[</span><span class="syntaxstring">"august"</span><span class="syntaxkeyword">,</span><span class="syntaxstring">"dan"</span><span class="syntaxkeyword">,</span><span class="syntaxstring">"tig"</span><span class="syntaxkeyword">]<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="syntaxdefault">b&nbsp;</span><span class="syntaxkeyword">=&nbsp;</span><span class="syntaxdefault">a</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">dclone<br />&nbsp;&nbsp;&nbsp;&nbsp;<br />&nbsp;&nbsp;&nbsp;&nbsp;puts&nbsp;</span><span class="syntaxstring">"a&nbsp;is;&nbsp;#{a.inspect}"<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="syntaxdefault">puts&nbsp;</span><span class="syntaxstring">"b&nbsp;is;&nbsp;#{b.inspect}"<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="syntaxdefault">puts&nbsp;</span><span class="syntaxstring">"changing&nbsp;a[1]&nbsp;to&nbsp;\"bob\""<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="syntaxdefault">a</span><span class="syntaxkeyword">[</span><span class="syntaxdefault">1</span><span class="syntaxkeyword">]=&nbsp;</span><span class="syntaxstring">"bob"<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="syntaxdefault">puts&nbsp;</span><span class="syntaxstring">"a&nbsp;is;&nbsp;#{a.inspect}"<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span class="syntaxdefault">puts&nbsp;</span><span class="syntaxstring">"b&nbsp;is;&nbsp;#{b.inspect}"<br /><br />&nbsp;&nbsp;</span><span class="syntaxdefault">end&nbsp;</span><span class="syntaxcomment">#&nbsp;module&nbsp;SomePlugin<br /></span><span class="syntaxdefault">end&nbsp;</span><span class="syntaxcomment">#&nbsp;Author's&nbsp;namespace<br />&nbsp;</span><span class="syntaxdefault"></span>

Any call to using() must occur within the TOPLEVEL_BINDING.
This restriction has been removed in later versions of Ruby 2.2+, and the experimental warning that is output on calls to refine has also been removed. (Ie, refinements are no longer experimental and calls to using can happen inside specific module and class scopes.)

If you want to see that all the elements of the arrays are different objects, you can iterate them and compare their object id numbers.

August

Thanks Dan,

So refine allows me to add my own operators to an existing class? That's a sweet (and dangerous) concept.

I'll have to put that on the back burner for now. I'm still working on basic Ruby.

Dan Rathbun

@august said:

So refine allows me to add my own operators to an existing class? That's a sweet (and dangerous) concept.

Refinements do not affect other people's scripts that do not "use" the refinement module. (They are only valid within the file that has the using call.)

Dan Rathbun

Another basic concept is the mixin module, which uses include() and extend().

In this case, in order to affect only the array you are using, you need to only "extend" the specific array instance object.

So, assume you have previously loaded a mixin module thus:

<span class="syntaxdefault">module August<br />  module DeepCopy<br /><br />    def dclone<br />      klone </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> self</span><span class="syntaxkeyword">.clone<br /></span><span class="syntaxdefault">      klone</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">clear<br />      self</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">each</span><span class="syntaxkeyword">{|</span><span class="syntaxdefault">v</span><span class="syntaxkeyword">|</span><span class="syntaxdefault"> klone </span><span class="syntaxkeyword"><<</span><span class="syntaxdefault"> v</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">dclone</span><span class="syntaxkeyword">}<br /></span><span class="syntaxdefault">      klone<br />    end<br /><br />  end </span><span class="syntaxcomment"># mixin module DeepCopy<br /></span><span class="syntaxdefault">end </span><span class="syntaxcomment"># Author's namespace&nbsp;</span><span class="syntaxdefault"></span>

Then you need to extend a specific array instance:

<span class="syntaxdefault">a </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> </span><span class="syntaxkeyword">[</span><span class="syntaxstring">"august"</span><span class="syntaxkeyword">,</span><span class="syntaxstring">"dan"</span><span class="syntaxkeyword">,</span><span class="syntaxstring">"tig"</span><span class="syntaxkeyword">]<br /><br /></span><span class="syntaxdefault">a</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">extend</span><span class="syntaxkeyword">(</span><span class="syntaxdefault">August</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">DeepCopy</span><span class="syntaxkeyword">)<br /><br /></span><span class="syntaxdefault">b </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> a</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">dclone</span>

August

Back to TIG's comment about plural vs. singular names for arrays, here is the way I'm naming things. In this context, the singular terms seem to work better for me, probably because I think of it as the mathematical notation P[sub:2dctu78y]0[/sub:2dctu78y], P[sub:2dctu78y]1[/sub:2dctu78y], ... P[sub:2dctu78y]N[/sub:2dctu78y].

=begin

          point[N]
                  x-------------x point[0]  angle[0] = angle_between vector[N], vector[0]
                     vector[N]   \
  vector[N] = point[N], point[0]  \
                                   \
                          vector[0] \
      vector[0] = point[0], point[1] \
                                      x point[1]  angle[1] = angle_between vector[0], vector[1]
                                     /
                          vector[1] /
    vector[1] = point[1], point[2] /
                                  /
                                 /
                                x point[2]  angle[2] = angle_between vector[1], vector[2]

=end