--- title: Ready Or Not, Here It Comes | daily.dev description: PHP 8.1 added return types to built-in interfaces like Iterator and IteratorAggregate, which broke PHPUnit's PHAR distribution. The root cause was that... canonical: https://daily.dev/posts/ready-or-not-here-it-comes-brbeh5tnh twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Ready Or Not, Here It Comes | daily.dev og:description: PHP 8.1 added return types to built-in interfaces like Iterator and IteratorAggregate, which broke PHPUnit's PHAR distribution. The root cause was that... og:url: https://daily.dev/posts/ready-or-not-here-it-comes-brbeh5tnh og:image: https://api.daily.dev/og/posts/bRbeH5tnh.png og:image:alt: Ready Or Not, Here It Comes og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Ready Or Not, Here It Comes **[PHPUnit Expert](https://daily.dev/sources/phpunit-expert)** · 8 min read · 0 upvotes · 0 comments ## Summary PHP 8.1 added return types to built-in interfaces like Iterator and IteratorAggregate, which broke PHPUnit's PHAR distribution. The root cause was that PHPUnit's PHAR used static preloading (a sorted list of require statements) to load all bundled code at startup, but PHP's compiler couldn't perform method compatibility checks when referenced classes hadn't been loaded yet. The fix combines static preloading with a dynamic autoloader fallback, so the compiler can resolve class dependencies during compatibility checks. The post also urges PHP developers to test their software against PHP 8.1 betas now, and advocates for treating PHP version upgrades as a routine operational procedure rather than a special project. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [PHP 8.4.23RC1 Ready for testing](https://daily.dev/posts/php-8-4-23rc1-ready-for-testing-4jahlleze) · externals.io · 0 upvotes · 0 comments --- Tags: [#php](https://daily.dev/tags/php), [#phpunit](https://daily.dev/tags/phpunit) [View this post on daily.dev](https://daily.dev/posts/ready-or-not-here-it-comes-brbeh5tnh) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Ready Or Not, Here It Comes","url":"https://daily.dev/posts/ready-or-not-here-it-comes-brbeh5tnh","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/ready-or-not-here-it-comes-brbeh5tnh"},"datePublished":"2026-03-31T13:34:22.011Z","dateModified":"2026-03-31T13:35:05.014Z","description":"PHP 8.1 added return types to built-in interfaces like Iterator and IteratorAggregate, which broke PHPUnit's PHAR distribution. 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