--- title: Intermediate collection avoidance | daily.dev description: Kotlin's collection API allows avoiding intermediate allocations by fusing operations. Using `joinToString { }` with a lambda instead of `map {... canonical: https://daily.dev/posts/intermediate-collection-avoidance-thvbqwgnk twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Intermediate collection avoidance | daily.dev og:description: Kotlin's collection API allows avoiding intermediate allocations by fusing operations. Using `joinToString { }` with a lambda instead of `map {... og:url: https://daily.dev/posts/intermediate-collection-avoidance-thvbqwgnk og:image: https://api.daily.dev/og/posts/THvbqWGNK.png og:image:alt: Intermediate collection avoidance 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. # Intermediate collection avoidance **[Jake Wharton](https://daily.dev/sources/jakewharton)** · 3 min read · 0 upvotes · 0 comments ## Summary Kotlin's collection API allows avoiding intermediate allocations by fusing operations. Using `joinToString { }` with a lambda instead of `map { }.joinToString()` eliminates the intermediate collection and iterator. Similarly, `Array(size) { }`, `IntArray(size) { }`, and `MutableList(size) { }` constructors accept lambdas that replace `map { }.toTypedArray()` patterns. Benchmarks show the lambda-based variants are significantly faster and allocate fewer bytes. The technique requires random-access backing structures to be effective and is best suited for internal library code. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: --- Tags: [#performance](https://daily.dev/tags/performance), [#android](https://daily.dev/tags/android), [#kotlin](https://daily.dev/tags/kotlin) [View this post on daily.dev](https://daily.dev/posts/intermediate-collection-avoidance-thvbqwgnk) ```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":"Intermediate collection avoidance","url":"https://daily.dev/posts/intermediate-collection-avoidance-thvbqwgnk","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/intermediate-collection-avoidance-thvbqwgnk"},"datePublished":"2026-07-05T07:13:57.338Z","dateModified":"2026-07-05T07:18:16.602Z","description":"Kotlin's collection API allows avoiding intermediate allocations by fusing operations. Using `joinToString { }` with a lambda instead of `map {...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/783b359bc344ce8763770516ac461830?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/783b359bc344ce8763770516ac461830?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Jake Wharton","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":"Jake Wharton","logo":"https://media.daily.dev/image/upload/logos/placeholder.jpg","url":"https://daily.dev/sources/jakewharton"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/intermediate-collection-avoidance-thvbqwgnk","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"performance,android,kotlin","timeRequired":"PT3M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Jake Wharton","item":"https://daily.dev/sources/jakewharton"},{"@type":"ListItem","position":3,"name":"Intermediate collection avoidance"}]} ```