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Date: Sun, 12 Aug 2012 19:14:46 -0600
Message-ID: <CAFMT4Nr-1HWgeKcjjRCXV726hTCW+E7md+97uBFmakTfG7PwgA@mail.gmail.com>
To: Brian Moon <brian@moonspot.net>
Cc: Nikita Popov <nikita.ppv@gmail.com>, PHP internals <internals@lists.php.net>
Content-Type: text/plain; charset=ISO-8859-1
Subject: Re: [PHP-DEV] [RFC] Generators
From: morrison.levi@gmail.com (Levi Morrison)

On Sun, Aug 12, 2012 at 5:56 PM, Brian Moon <brian@moonspot.net> wrote:
> On 8/12/12 5:33 PM, Levi Morrison wrote:
>>
>> On Sun, Aug 12, 2012 at 2:08 PM, Brian Moon <brian@moonspot.net> wrote:
>>>
>>> Do you have a good example usage other than a file? I don't find
>>> fopen/fgets/fclose all that complicated. What are the other valid use cases
>>> for such a thing?
>>
>>
>> One fabulous use case is creating an iterator for a Binary Search
>> Tree.  A post order done without generators looks like:
>>
>> https://github.com/morrisonlevi/PHP-Datastructures/blob/master/src/Spl/PostOrderIterator.php.
>>   An iterator using a generator looks something like:
>>
>>      public function getIterator() {
>>          if ($this->left) yield* $this->left;
>>          yield $this->value;
>>          if ($this->right) yield* $this->right;
>>      }
>>
>> This is 5 lines.  The fully commented version of the post-order
>> iterator previously mentioned is 106 lines of code and is considerably
>> harder to understand.
>
>
> Well, it's 52 lines, not 106. The 5 lines above are not commented nor are
> they spaced at all like the ones in the class.

No, Brian, it is 106 lines of actual code I would find in the wild.
And sure, I'd have spaced the generator code more like:
     public function getIterator() {
          if ($this->left) {
              yield* $this->left;
          }

          if ($this->right) {
              yield* $this->right;
          }

          yield $this->value;
      }

However, that's 11 lines of code compared to 106.

> In the above example, what
> sets $this->right? or $this->left?

Iterators don't set $this->right and $this->left; they only traverse the tree.

> I don't consider this a very good example.
That's fine.  You are entitled to your opinion. However, you didn't
have to figure out the 106 lines of code that is the Post-Order
iterator.  That was a NIGHTMARE and I'm still not 100% confident that
it works as it is supposed to.  The generator, on the other hand, is
simple and follows the definition very closely.  MUCH better.