--- title: New in Symfony 8.2: Generics and Stricter Types in the... description: Symfony 8.2 makes the Serializer and TypeInfo components understand generics and arrays of union types from PHPDoc annotations, and enforces them more... canonical: https://daily.dev/posts/new-in-symfony-8-2-generics-and-stricter-types-in-the-serializer-symfony-blog--txfzewrmy twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: New in Symfony 8.2: Generics and Stricter Types in the Serializer (Symfony Blog) | daily.dev og:description: Symfony 8.2 makes the Serializer and TypeInfo components understand generics and arrays of union types from PHPDoc annotations, and enforces them more... og:url: https://daily.dev/posts/new-in-symfony-8-2-generics-and-stricter-types-in-the-serializer-symfony-blog--txfzewrmy og:image: https://api.daily.dev/og/posts/TxFzEWRMy.png og:image:alt: New in Symfony 8.2: Generics and Stricter Types in the Serializer (Symfony Blog) 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. # New in Symfony 8.2: Generics and Stricter Types in the Serializer (Symfony Blog) **[Symfony](https://daily.dev/sources/symfony)** · 5 min read · 0 upvotes · 0 comments ## Summary Symfony 8.2 makes the Serializer and TypeInfo components understand generics and arrays of union types from PHPDoc annotations, and enforces them more strictly. The Serializer now resolves template types like 'Page' so denormalized collections contain real objects instead of arrays. It also denormalizes elements inside 'list', though a non-matching element now throws an exception instead of passing through unchanged. A 'list' property that receives a JSON object now triggers a deprecation in 8.2 and will throw 'NotNormalizableValueException' in Symfony 9.0. A new 'Type::getMismatches()' method reports exactly which values and paths fail to match a type. Generic resolution requires PropertyInfo's 'PhpStanExtractor' and the 'phpstan/phpdoc-parser' package. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How does Symfony 8.2's Serializer handle denormalizing a generic class like Page? Symfony 8.2 resolves the template type declared on the property holding the generic object, for example reading 'Page' from a property typed that way, resolving 'T' to 'Product', and using that type when denormalizing the inner 'Page::$items' array. This works with nullable and nested generics, multiple templates, union types, constructor arguments, and collections like 'list>', but requires PropertyInfo's PhpStanExtractor and the phpstan/phpdoc-parser package. _daily.dev helps PHP developers track Symfony serializer changes like this before upgrading production code._ ### Why does my Symfony Serializer throw an exception when denormalizing a list of union types instead of returning the raw array? In Symfony 8.2, denormalizing a collection typed as 'list' now matches each element against the union and converts it to the correct class, which is a behavior change from prior versions that left such elements as raw arrays. An element matching no member of the union, or a key that doesn't match the expected key type, now throws an exception instead of passing through unchanged. _developers adapting to breaking serializer changes can follow Symfony upgrade details on daily.dev._ ### Why does deserializing a JSON object into a list property in Symfony trigger a deprecation warning? Because a 'list' type requires consecutive integer keys starting at zero, while a JSON object like '{"5":"foo","1":"bar"}' doesn't meet that promise. Symfony 8.2 still accepts it but raises a deprecation notice; Symfony 9.0 will throw a 'NotNormalizableValueException' instead. The fix is to send a JSON array like '["foo","bar"]' or declare a different array type if the keys carry meaning. _daily.dev keeps PHP teams ahead of Symfony deprecations before they become breaking changes in 9.0._ ## Similar posts on daily.dev - [New in Symfony 8.2: JsonSchema Component \(Symfony Blog\)](https://daily.dev/posts/new-in-symfony-8-2-jsonschema-component-symfony-blog--eps4sbfhs) · Symfony · 3 upvotes · 0 comments - [CakePHP is now fully generics-able – DerEuroMark](https://daily.dev/posts/cakephp-is-now-fully-generics-able-dereuromark-cwz39vwo6) · DerEuroMark · 3 upvotes · 0 comments - [New in Symfony 8.1: Improved JSON Streaming and Querying \(Symfony Blog\)](https://daily.dev/posts/new-in-symfony-8-1-improved-json-streaming-and-querying-symfony-blog--doadnpbjr) · Symfony · 4 upvotes · 0 comments - [New in Symfony 8.2: Performance Improvements \(Symfony Blog\)](https://daily.dev/posts/new-in-symfony-8-2-performance-improvements-symfony-blog--ef0ps6tns) · Symfony · 4 upvotes · 0 comments - [New in Symfony 8.2: More Flexible Serialization Groups \(Symfony Blog\)](https://daily.dev/posts/new-in-symfony-8-2-more-flexible-serialization-groups-symfony-blog--s7l6m91ib) · Symfony · 2 upvotes · 0 comments --- Tags: [#php](https://daily.dev/tags/php), [#symfony](https://daily.dev/tags/symfony), [#type-systems](https://daily.dev/tags/type-systems), [#phpstan](https://daily.dev/tags/phpstan) [View this post on daily.dev](https://daily.dev/posts/new-in-symfony-8-2-generics-and-stricter-types-in-the-serializer-symfony-blog--txfzewrmy) ```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":"New in Symfony 8.2: Generics and Stricter Types in the Serializer (Symfony Blog)","url":"https://daily.dev/posts/new-in-symfony-8-2-generics-and-stricter-types-in-the-serializer-symfony-blog--txfzewrmy","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/new-in-symfony-8-2-generics-and-stricter-types-in-the-serializer-symfony-blog--txfzewrmy"},"datePublished":"2026-10-27T09:10:41.908Z","dateModified":"2026-10-27T09:11:17.006Z","description":"Symfony 8.2 makes the Serializer and TypeInfo components understand generics and arrays of union types from PHPDoc annotations, and enforces them more...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/327b244859fddae8f3a20d0225898aa0?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/327b244859fddae8f3a20d0225898aa0?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Symfony","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Symfony","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/cc07051b7112472f9729e73c14660a64","url":"https://daily.dev/sources/symfony"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/new-in-symfony-8-2-generics-and-stricter-types-in-the-serializer-symfony-blog--txfzewrmy","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"php,symfony,type-systems,phpstan","timeRequired":"PT5M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Symfony","item":"https://daily.dev/sources/symfony"},{"@type":"ListItem","position":3,"name":"New in Symfony 8.2: Generics and Stricter Types in the Serializer (Symfony Blog)"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/new-in-symfony-8-2-generics-and-stricter-types-in-the-serializer-symfony-blog--txfzewrmy#faq","mainEntity":[{"@type":"Question","name":"How does Symfony 8.2's Serializer handle denormalizing a generic class like Page\u003cProduct\u003e?","acceptedAnswer":{"@type":"Answer","text":"Symfony 8.2 resolves the template type declared on the property holding the generic object, for example reading 'Page\u003cProduct\u003e' from a property typed that way, resolving 'T' to 'Product', and using that type when denormalizing the inner 'Page::$items' array. 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