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<title>Crystal (programming language)</title>

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Crystal (programming language)

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</style><table class="infobox vevent"><tbody><tr><th colspan="2" class="infobox-above" style="background-color:#e0e0e0;">Crystal</th></tr><tr><td colspan="2" class="infobox-image"></td></tr><tr><th scope="row" class="infobox-label"><a href="Programming_paradigm" title="Programming paradigm">Paradigm</a></th><td class="infobox-data"><a href="Multi-paradigm_programming_language" class="mw-redirect" title="Multi-paradigm programming language">Multi-paradigm</a>: <a href="Object-oriented_programming" title="Object-oriented programming">object-oriented</a>, <a href="Concurrent_computing" title="Concurrent computing">concurrent</a></td></tr><tr><th scope="row" class="infobox-label"><a href="Software_design" title="Software design">Designed by</a></th><td class="infobox-data">Ary Borenszweig, Juan Wajnerman, Brian Cardiff</td></tr><tr><th scope="row" class="infobox-label"><a href="Software_developer" class="mw-redirect" title="Software developer">Developer</a></th><td class="infobox-data organiser">Manas Technology Solutions</td></tr><tr><th scope="row" class="infobox-label">First appeared</th><td class="infobox-data">June 19, 2014 (2014-06-19)<a href="#cite_note-1">[1]</a></td></tr><tr><td colspan="2" class="infobox-full-data"></td></tr><tr><th scope="row" class="infobox-label" style="white-space: nowrap;"><a href="Software_release_life_cycle" title="Software release life cycle">Stable release</a></th><td class="infobox-data"><div style="margin:0px;">1.16.3<a href="#cite_note-wikidata-074292ab12fcdf6fa455f20ca57a14e6a4b89731-v20-2">[2]</a>

/ 12 May 2025 (12 May 2025)</div></td></tr><tr style="display:none"><td colspan="2">

</td></tr><tr><th scope="row" class="infobox-label"><a href="Type_system" title="Type system">Typing discipline</a></th><td class="infobox-data"><a href="Type_system#Static_type_checking" title="Type system">static</a>, <a href="Type_system#Inferred_type_checking" title="Type system">inferred</a>, <a href="Nominal_type_system" title="Nominal type system">nominal</a>, <a href="Duck_typing" title="Duck typing">duck</a></td></tr><tr><th scope="row" class="infobox-label">Implementation language</th><td class="infobox-data">Crystal</td></tr><tr><th scope="row" class="infobox-label"><a href="Computing_platform" title="Computing platform">Platform</a></th><td class="infobox-data"><a href="IA-32" title="IA-32">IA-32</a> (i386), <a href="X86-64" title="X86-64">x86-64</a>, <a href="AArch64" title="AArch64">AArch64</a><a href="#cite_note-platform-support-3">[3]</a></td></tr><tr><th scope="row" class="infobox-label"><a href="Operating_system" title="Operating system">OS</a></th><td class="infobox-data"><a href="Linux" title="Linux">Linux</a>, <a href="MacOS" title="MacOS">macOS</a>, <a href="FreeBSD" title="FreeBSD">FreeBSD</a>, <a href="OpenBSD" title="OpenBSD">OpenBSD</a>, <a href="Microsoft_Windows" title="Microsoft Windows">Windows</a><a href="#cite_note-platform-support-3">[3]</a></td></tr><tr><th scope="row" class="infobox-label"><a href="Software_license" title="Software license">License</a></th><td class="infobox-data"><a href="Apache_License_2.0" class="mw-redirect" title="Apache License 2.0">Apache License 2.0</a></td></tr><tr><th scope="row" class="infobox-label"><a href="Filename_extension" title="Filename extension">Filename extensions</a></th><td class="infobox-data">.cr</td></tr><tr><th scope="row" class="infobox-label">Website</th><td class="infobox-data"><a rel="nofollow" class="external text" href="https://crystal-lang.org">crystal-lang.org</a></td></tr><tr><th colspan="2" class="infobox-header" style="background-color: #EEEEEE;">Influenced by</th></tr><tr><td colspan="2" class="infobox-full-data"><a href="Ruby_(programming_language)" title="Ruby (programming language)">Ruby</a>, <a href="Go_(programming_language)" title="Go (programming language)">Go</a><a href="#cite_note-go_multithread-4">[4]</a></td></tr></tbody></table>

Crystal is a <a href="High-level_programming_language" title="High-level programming language">high-level</a> <a href="General-purpose_programming_language" title="General-purpose programming language">general-purpose</a>, <a href="Object-oriented_programming" title="Object-oriented programming">object-oriented programming</a> language, designed and developed by Ary Borenszweig, Juan Wajnerman, Brian Cardiff and more than 400 contributors.<a href="#cite_note-contributors-5">[5]</a> With syntax inspired by the language <a href="Ruby_(programming_language)" title="Ruby (programming language)">Ruby</a>,<a href="#cite_note-rel_0.18.0-6">[6]</a> it is a <a href="Compiled_language" title="Compiled language">compiled language</a> with <a href="Type_system#Static_type_checking" title="Type system">static type-checking</a>, but specifying the types of variables or method arguments is generally unneeded. Types are resolved by an advanced global <a href="Type_inference" title="Type inference">type inference</a> algorithm.<a href="#cite_note-type-inference-i-7">[7]</a><a href="#cite_note-devm-8">[8]</a> Crystal

is currently in active development. It is released as <a href="Free_and_open-source_software" title="Free and open-source software">free and open-source software</a> under the <a href="Apache_License" title="Apache License">Apache License</a> version 2.0.

<div class="mw-heading mw-heading2"><h2 id="History">History</h2></div>

Work on the language began in June 2011,<a href="#cite_note-story-9">[9]</a> with the aim of merging the elegance and productivity of Ruby with the speed, efficiency, and type safety of a compiled language.<a href="#cite_note-why_crystal-10">[10]</a><a href="#cite_note-story-9">[9]</a> Initially named Joy, it was quickly renamed to Crystal.<a href="#cite_note-story-9">[9]</a>

The Crystal compiler was first written in Ruby, but later rewritten in Crystal, thus becoming <a href="Self-hosting_(compilers)" title="Self-hosting (compilers)">self-hosting</a>, as of November 2013.<a href="#cite_note-goodbye_ruby-11">[11]</a> The first official version was released in June 2014.<a href="#cite_note-rel_0.1.0-12">[12]</a> In July 2016, Crystal joined the <a href="TIOBE_index" title="TIOBE index">TIOBE index</a>.

<div class="mw-heading mw-heading2"><h2 id="Description">Description</h2></div>

Although resembling the Ruby language in syntax, Crystal compiles to much more efficient native code using an <a href="LLVM" title="LLVM">LLVM</a> backend, at the cost of precluding the dynamic aspects of Ruby. The advanced global type inference used by the Crystal compiler, combined with <a href="Union_type" title="Union type">union types</a>, gives it more the feel of a higher-level scripting language than many other comparable programming languages. It has automated garbage collection and offers a <a href="Boehm_garbage_collector" title="Boehm garbage collector">Boehm collector</a>. Crystal possesses a macro system and supports generics as well as method and operator overloading. Its concurrency model is inspired by <a href="Communicating_sequential_processes" title="Communicating sequential processes">communicating sequential processes</a> (CSP) and implements lightweight fibers and channels (for interfiber communication), inspired by <a href="Go_(programming_language)" title="Go (programming language)">Go</a>.<a href="#cite_note-go_multithread-4">[4]</a>

<div class="mw-heading mw-heading2"><h2 id="Examples">Examples</h2></div>

<div class="mw-heading mw-heading3"><h3 id="Hello_World">Hello World</h3></div>

This is the simplest way to write the <a href="%22Hello%2C_World!%22_program" title=""Hello, World!" program">Hello World</a> program in Crystal:

<div class="mw-highlight mw-highlight-lang-crystal mw-content-ltr" dir="ltr"><pre>puts "Hello World!"

</pre></div>

The same as in Ruby.

Or using an <a href="Object-oriented_programming" title="Object-oriented programming">object-oriented programming</a> style:

<div class="mw-highlight mw-highlight-lang-crystal mw-content-ltr" dir="ltr"><pre>class Greeter

def initialize(@name : String)

end

def salute

puts "Hello #{@name}!"

end

end

g = Greeter.new("world")

g.salute

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="HTTP_server">HTTP server</h3></div>

<div class="mw-highlight mw-highlight-lang-crystal mw-content-ltr" dir="ltr"><pre>require "http/server"

server = HTTP::Server.new do |context|

context.response.content_type = "text/plain"

context.response.print "Hello world! The time is #{Time.local}"

end

server.bind_tcp("0.0.0.0", 8080)

puts "Listening on http://0.0.0.0:8080"

server.listen

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="TCP_echo_server">TCP echo server</h3></div>

<div class="mw-highlight mw-highlight-lang-crystal mw-content-ltr" dir="ltr"><pre>require "socket"

def handle_client(client)

message = client.gets

client.puts message

end

server = TCPServer.new("localhost", 1234)

while client = server.accept?

spawn handle_client(client)

end

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="Type_inference_and_union_types">Type inference and union types</h3></div>

The following code defines an array containing different types with no usable common ancestor. Crystal automatically creates a union type out of the types of the individual items.

<div class="mw-highlight mw-highlight-lang-crystal mw-content-ltr" dir="ltr"><pre>desired_things = [:unicorns, "butterflies", 1_000_000]

p typeof(desired_things.first) # typeof returns the compile time type, here (Symbol | String | Int32)

p desired_things.first.class # the class method returns the runtime type, here Symbol

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="Concurrency">Concurrency</h3></div>

Channels can be used to communicate between fibers, which are initiated using the keyword <code>spawn</code>.

<div class="mw-highlight mw-highlight-lang-crystal mw-content-ltr" dir="ltr"><pre>channel = Channel(Int32).new

spawn do

puts "Before first send"

channel.send(1)

puts "Before second send"

channel.send(2)

end

puts "Before first receive"

value = channel.receive

puts value # => 1

puts "Before second receive"

value = channel.receive

puts value # => 2

</pre></div>

<div class="mw-heading mw-heading2"><h2 id="Adoption">Adoption</h2></div>

In 2020, it was reported that the infotainment units in vehicles produced by <a href="Nikola_Corporation" title="Nikola Corporation">Nikola Corporation</a> were written in Crystal.<a href="#cite_note-13">[13]</a> Much of the backend of the <a href="Kagi_(search_engine)" title="Kagi (search engine)">Kagi search engine</a> is written with Crystal.<a href="#cite_note-14">[14]</a>

<div class="mw-heading mw-heading2"><h2 id="Further_reading">Further reading</h2></div>

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</style><cite id="CITEREFSt._LaurentBalbaert2019" class="citation cs2">St. Laurent, Simon; Balbaert, Ivo (February 1, 2019), <a rel="nofollow" class="external text" href="https://pragprog.com/book/crystal/programming-crystal">Programming Crystal</a> (P1.0 ed.), <a href="Pragmatic_Bookshelf" class="mw-redirect" title="Pragmatic Bookshelf">Pragmatic Bookshelf</a>, <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-1-68050-286-2</bdi></cite></li>

<li><cite id="CITEREFDietrichBernal2022" class="citation cs2">Dietrich, George; Bernal, Guilherme (May 27, 2022), Crystal Programming, <a href="Packt_Publishing" class="mw-redirect" title="Packt Publishing">Packt Publishing</a>, <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-1801818674</bdi></cite></li>

<li><cite id="CITEREFWartala2016" class="citation cs2 cs1-prop-foreign-lang-source">Wartala, Ramon (March 2016), <a rel="nofollow" class="external text" href="https://www.linux-magazin.de/ausgaben/2016/03/crystal/">"Die Ruby-artige Programmiersprache Crystal"</a> [The Ruby-like programming language Crystal], <a href="Linux_Magazine" title="Linux Magazine">Linux Magazin</a> (in German), no. 3/2016, <a href="ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/1432-640X">1432-640X</a></cite></li></ul>

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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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<li id="cite_note-1"><a href="#cite_ref-1">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://crystal-lang.org/2014/06/19/crystal-0.1.0-released.html">"Crystal 0.1.0 released!"</a>. crystal-lang. 19 June 2014.</cite>

</li>

<li id="cite_note-wikidata-074292ab12fcdf6fa455f20ca57a14e6a4b89731-v20-2"><a href="#cite_ref-wikidata-074292ab12fcdf6fa455f20ca57a14e6a4b89731-v20_2-0">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://github.com/crystal-lang/crystal/releases/tag/1.16.3">"Release 1.16.3"</a>. 12 May 2025. Retrieved 25 May 2025.</cite>

</li>

<cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://crystal-lang.org/reference/platform_support.html">"Crystal Platform Support"</a>. crystal-lang.org.</cite>

</li>

<li id="cite_note-go_multithread-4">^ <a href="#cite_ref-go_multithread_4-0">a</a> <a href="#cite_ref-go_multithread_4-1">b</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://forum.crystal-lang.org/t/crystal-multithreading-support/6622/19">"Crystal multithreading support"</a>. 23 February 2024.</cite>

</li>

<cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://github.com/crystal-lang/crystal/graphs/contributors">"Contributors"</a>. Retrieved July 25, 2019 – via <a href="GitHub" title="GitHub">GitHub</a>.</cite>

</li>

<cite id="CITEREFBorenszweig2016" class="citation web cs1">Borenszweig, Ary (June 16, 2016). <a rel="nofollow" class="external text" href="http://crystal-lang.org/2016/06/14/crystal-0.18.0-released.html#comment-2732771703">"Crystal 0.18.0 released!"</a>. crystal-lang.org.</cite>

</li>

<cite id="CITEREFBrian_J.2013" class="citation web cs1">Brian J., Cardiff (September 9, 2013). <a rel="nofollow" class="external text" href="http://crystal-lang.org/2013/09/23/type-inference-part-1.html">"Type inference part 1"</a>. crystal-lang.org.</cite>

</li>

<cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://devm.io/ruby/crystal-ruby-programming">"Programming with Crystal: 'A language for humans and computers'"</a>. devm.io. July 3, 2023.</cite>

</li>

<cite id="CITEREFDavid2016" class="citation web cs1">David, María Inti (April 1, 2016). <a rel="nofollow" class="external text" href="https://manas.tech/blog/2016/04/01/the-story-behind-crystal/">"The story behind #CrystalLang"</a>. manas.tech.</cite>

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<cite id="CITEREFHsieh2015" class="citation web cs1">Hsieh, Adler (September 20, 2015). <a rel="nofollow" class="external text" href="https://adlerhsieh.com/p/why-use-crystal-lang">"Why Crystal programming language?"</a>. adlerhsieh.com.</cite>

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<cite id="CITEREFBorenszweig2013" class="citation web cs1">Borenszweig, Ary (November 14, 2013). <a rel="nofollow" class="external text" href="https://crystal-lang.org/2013/11/14/good-bye-ruby-thursday.html">"Good bye Ruby Thursday"</a>. crystal-lang.org.</cite>

</li>

<cite id="CITEREFBorenszweig2014" class="citation web cs1">Borenszweig, Ary (June 19, 2014). <a rel="nofollow" class="external text" href="https://crystal-lang.org/2014/06/19/crystal-0.1.0-released.html">"Crystal 0.1.0 released!"</a>. crystal-lang.org.</cite>

</li>

<li id="cite_note-13"><a href="#cite_ref-13">^</a> <cite id="CITEREFPettinati2020" class="citation web cs1">Pettinati, Martin (11 February 2020). <a rel="nofollow" class="external text" href="https://manas.tech/blog/2020/02/11/nikola-motor-company/">"Nikola Motor Company: Crystal powered dashboards on the trucks of the future | Manas.Tech"</a>. Manas Technology Solutions.</cite>

</li>

<li id="cite_note-14"><a href="#cite_ref-14">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.youtube.com/watch?v=r7t9xPajjTM">"Zac Nowicki – Tales from Kagi | CrystalConf 2023"</a>. 13 November 2023.</cite>

</li>

</ol></div></div>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://crystal-lang.org">Official website</a></li>

<li><a rel="nofollow" class="external text" href="https://crystal-lang.org/reference/">Documentation</a></li>

<li><a rel="nofollow" class="external text" href="https://github.com/crystal-lang">Crystal-lang</a> on <a href="GitHub" title="GitHub">GitHub</a></li>

<li><a rel="nofollow" class="external text" href="https://reddit.com/r/crystal_programming">/r/crystal_programming subreddit</a></li>

<li><a rel="nofollow" class="external text" href="https://crystal-ann.com">Crystal Announcements</a></li></ul></div><div><div class="zim-footer">

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