TypeError: can't convert into Array

thomthom

@jim said:

I think Enumerable requires that your class implement a .each method. Some Enumerable methods also need a <=> method (comparison) defined.

I do have an .each method implemented. But in any case would that matter for converting to an Array?

I manually added an #to_a method to my that returns an array. So I don't understand why it raises this error...

Jim

You need to yield in your .each iterator.

Something like this (not tested.)

@entities.each{|e| yield(e)}

See also: block_given?

Here's a related article about the performance of passing blocks: http://mudge.github.com/2011/01/26/passing-blocks-in-ruby-without-block.html

Dan Rathbun

@thomthom said:

I manually added an #to_a method to my [class] that returns an array. So I don't understand why it raises this error...

Is the superclass one of those API C++ collection classes ? Most of these give us problems when we try to subclass them.

thomthom

@jim said:

You need to yield in your .each iterator.

It does that.

But I fail to see why .each got to do with converting to an array when I have a .to_a method ... ? I've been searching for info on it, but I cannot find anything.

Jim

@thomthom said:

It does that.

Sorry, I was looking at your latest bitbucket repo, which must not be your latest version.

thomthom

No - it's still on my computer. A larger rewrite. The one at the repo was just an early framework WIP.

thomthom

A simplified example:

<span class="syntaxdefault"></span><span class="syntaxkeyword">class&nbsp;</span><span class="syntaxdefault">Foo</span><span class="syntaxkeyword">;&nbsp;</span><span class="syntaxdefault">def&nbsp;to_a</span><span class="syntaxkeyword">;&nbsp;[</span><span class="syntaxdefault">1</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">2</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">3</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">4</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">5</span><span class="syntaxkeyword">];&nbsp;</span><span class="syntaxdefault">end</span><span class="syntaxkeyword">;&nbsp;</span><span class="syntaxdefault">end</span><span class="syntaxkeyword">;<br /></span><span class="syntaxdefault">nil<br /><br />f</span><span class="syntaxkeyword">=</span><span class="syntaxdefault">Foo</span><span class="syntaxkeyword">.new<br /></span><span class="syntaxcomment">#<Foo;0x15259760><br /><br /></span><span class="syntaxdefault">x</span><span class="syntaxkeyword">=[</span><span class="syntaxdefault">3</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">4</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">5</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">6</span><span class="syntaxkeyword">]<br />[</span><span class="syntaxdefault">3</span><span class="syntaxkeyword">,&nbsp;</span><span class="syntaxdefault">4</span><span class="syntaxkeyword">,&nbsp;</span><span class="syntaxdefault">5</span><span class="syntaxkeyword">,&nbsp;</span><span class="syntaxdefault">6</span><span class="syntaxkeyword">]<br /><br /></span><span class="syntaxdefault">x&nbsp;</span><span class="syntaxkeyword">|&nbsp;</span><span class="syntaxdefault">f<br />Error</span><span class="syntaxkeyword">;&nbsp;</span><span class="syntaxcomment">#<TypeError;&nbsp;(eval);155;in&nbsp;`|';&nbsp;can't&nbsp;convert&nbsp;Foo&nbsp;into&nbsp;Array><br /></span><span class="syntaxkeyword">(eval);</span><span class="syntaxdefault">155<br /></span><span class="syntaxkeyword">(eval);</span><span class="syntaxdefault">155</span>

Off course, x | f.to_a works, but since the error message indicate some conversion was tried, I wonder why the .to_a method wasn't used.

Jim

use .to_ary although I don't have a good explanation yet.

class Foo
  def to_ary
    [1,2,3,4,5]
  end
end

This is as close to an explanation as I could find: http://stackoverflow.com/questions/766712/make-an-object-behave-like-an-array-for-parallel-assignment-in-ruby/768201#768201

thomthom

Thanks!

Class: Array (Ruby 1.8.6)

Class : Array - Ruby 1.8.6

(www.ruby-doc.org)

@unknownuser said:

Returns a new array. In the first form, the new array is empty. In the second it is created with size copies of obj (that is, size references to the same obj). The third form creates a copy of the array passed as a parameter (the array is generated by calling to_ary on the parameter). In the last form, an array of the given size is created. Each element in this array is calculated by passing the element’s index to the given block and storing the return value

So it appears what happens is not that f.to_a is called, but instead Array.new( f ) - and Array.new uses .to_ary .

Dan Rathbun

@thomthom said:

So it appears what happens is not that f.to_a is called, but instead Array.new( f ) - and Array.new uses .to_ary .

Actually (if you use the CHM Ruby refdoc,) the source shows that the #| method explicitly calls:
%(#0000BF)[arg2 = to_ary(arg2);]
ie, it makes a copy of the second arg to use locally (within its body.)