Crystal (programming language)


Crystal is a general-purpose, object-oriented programming language, designed and developed by Ary Borenszweig, Juan Wajnerman, Brian Cardiff and more than 300 contributors. With syntax inspired by the language Ruby, it is a compiled language with static type-checking, but specifying the types of variables or method arguments is generally unneeded. Types are resolved by an advanced global type inference algorithm. Crystal
is currently in active development. It is released as free and open-source software under the Apache License version 2.0.

History

Work on the language began in June 2011, with the purpose of creating a language with the elegance and productivity of Ruby and the speed, efficiency, and type safety of a compiled language. Initially named Joy, it was quickly renamed to Crystal.
The Crystal compiler was first written in Ruby, but later rewritten in Crystal, thus becoming self-hosting, as of November 2013. The first official version was released in June 2014. In July 2016, Crystal joined the TIOBE index.

Description

Although resembling the Ruby language in syntax, Crystal compiles to much more efficient native code using an LLVM backend, at the cost of precluding the dynamic aspects of Ruby. However, the advanced global type inference used by the Crystal compiler, combined with the use of union types, gives Crystal the feel of a higher-level scripting language more so than many other comparable programming languages. The language has automated garbage collection and currently offers a Boehm collector. Crystal possesses a macro system and supports generics, and method and operator overloading. Crystal's concurrency model is inspired by communicating sequential processes and implements light-weight fibers and channels inspired by the language Go.

Examples

Hello World

This is the simplest way to write the Hello World program in Crystal:

puts "Hello World!"

The same as in Ruby.
Or using an object-oriented programming style:

class Greeter
def initialize
end
def salute
puts "Hello #!"
end
end
g = Greeter.new
g.salute

HTTP server


require "http/server"
server = HTTP::Server.new do |context|
context.response.content_type = "text/plain"
context.response.print "Hello world! The time is #"
end
server.bind_tcp
puts "Listening on http://0.0.0.0:8080"
server.listen

TCP echo server


require "socket"
def handle_client
message = client.gets
client.puts message
end
server = TCPServer.new
while client = server.accept?
spawn handle_client
end

Type inference and union types

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.

desired_things =
p typeof # typeof returns the compile time type, here
p desired_things.first.class # the class method returns the runtime type, here Symbol

Concurrency

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

channel = Channel.new
spawn do
puts "Before first send"
channel.send
puts "Before second send"
channel.send
end
puts "Before first receive"
value = channel.receive
puts value # => 1
puts "Before second receive"
value = channel.receive
puts value # => 2