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Can someone explain how the image helper works in Magento and if the following two lines are identical? They appear to be identical strings when I run var_dump($temp), but memory usage says otherwise on certain products (outside of the scope of this question, but it happens on certain products and casting the string alleviates the problem).

$temp = $this->helper('catalog/image')->init($product, 'small_image')->resize(135);

$temp = (string)$this->helper('catalog/image')->init($product, 'small_image')->resize(135);
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Those 2 lines are not identical.
After the first line $temp will be an instance of Mage_Catalog_Helper_Image. This is because the resize method returns the currend object.

After the second line $temp will be a string.
When casting an object to a string it's the same as calling $object->__toString();
You can take a look at the Mage_Catalog_Helper_Image::__toString() methods. This is the one that actually creates the cached, resized image if it doesn't exist and returns the url of the image.

About the memory usage, I cant say much. What are you doing with $temp after the lines above? Maybe you do something that reaches the memory limit.

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  • Ah, does __toStrign() work the same for string-casting inside PHP and when echoing in HTML?
    – laketuna
    Commented Sep 17, 2013 at 20:22
  • Regarding the memory usage, simply assigning $this->helper()->... to a variable allocates ~500MB of memory on certain products. I have a post here: magento.stackexchange.com/questions/8113/…. But I do need to run some more tests to cases.
    – laketuna
    Commented Sep 17, 2013 at 20:24
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    when calling echo on an object PHP tries to convert it to string so it calls the same __toString method.
    – Marius ♦
    Commented Sep 17, 2013 at 20:27
  • Now I remember about the magic function.. I seem to regularly forget about this. Def need to use need to use OOP more. I see it in Mage_Catalog_Helper_Image where it returns the string URL.
    – laketuna
    Commented Sep 17, 2013 at 20:33
  • if you have to manipulate the url of the cached resized image, like doing a substr match and editing the url, it will be more efficient to cast the helper image object to string. Otherwise every time that substr is called on the object a __toString() is called, which affects performance quite a bit if you do it often.
    – Pitt
    Commented Aug 3, 2016 at 16:11

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