Opaque Objects & GdImage/CURLHandle

TL;DR

Explanation

Before PHP 8.0, many extensions returned resource types (is_resource() check, no type hints). PHP 8.0+ returns typed objects: imagecreatetruecolor() returns GdImage, curl_init() returns CurlHandle, xml_parser_create() returns XMLParser. These are opaque — you can't inspect their internals — but they're proper objects with type hints and are accepted by instanceof. Old code using is_resource() checks breaks. Type hints now possible: function process(GdImage $image). These objects are still reference-counted and freed when no longer referenced, similar to resources.

Common Misconception

Why It Matters

Common Mistakes

• Using is_resource() on GdImage/CurlHandle in PHP 8.0+ — always returns false.
• Not type-hinting function parameters accepting GdImage/CurlHandle.
• Trying to clone or serialize opaque objects — not supported.

Code Examples

$image = imagecreatetruecolor(100, 100);
if (!is_resource($image)) { // Always false in PHP 8!
    throw new Exception('Failed to create image');
}

$image = imagecreatetruecolor(100, 100);
if (!($image instanceof \GdImage)) {
    throw new \RuntimeException('Failed to create image');
}

function applyFilter(\GdImage $img, int $filter): void {
    imagefilter($img, $filter);
}

References

• ↗ https://www.php.net/manual/en/migration80.incompatible.php

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