Crystal (programming language)

Crystal is a general-purpose, object-oriented programming language designed and developed by Ary Borenszweig and Juan Wajnerman and over one-hundred listed contributors. Crystal is developed as open source software (under the Apache License, Version 2.0) with syntax inspired by Ruby. The language is statically type-checked but does not require that the type of variables or method arguments be specified. This is the result of advanced global type inference. Its first official release was in June 2014. While the original Crystal compiler was written in Ruby, in 2013 a new compiler written using the Crystal programming language itself was released. The current release version is 0.17 and the language is in an active development phase.

Description

Although resembling the Ruby programming language in syntax, Crystal compiles to much more efficient native code using an LLVM backend, at the cost of disallowing the dynamic aspects of Ruby. However, the advanced global type inference used by the Crystal compiler, combined with the usage of union types, give Crystal the feel of a higher-level scripting language than many other comparable programming languages. Recent benchmarks have demonstrated that Crystal has a performance broadly similar to C for a wide range of computing tasks. 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 (CSP), and implements light-weight fibers and channels (for communicating between fibers) inspired by the Go programming language.

Examples

Hello World

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

puts "Hello World!"

Or using an object-oriented programming style:

class Greeter
  def initialize(name)
    @name = name.capitalize
  end

  def salute
    puts "Hello #{@name}!"
  end
end

g = Greeter.new("world")
g.salute

HTTP Server

require "http/server"

server = HTTP::Server.new(8080) do |context|
  context.response.content_type = "text/plain"
  context.response.print "Hello world! The time is #{Time.now}"
end

puts "Listening on http://0.0.0.0:8080"
server.listen

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 = [:unicorns, "butterflies", 1_000_000]
p typeof(desired_things.first) # typeof returns the compile time type, here (Int32 | String | Symbol)
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 'spawn' keyword.

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

External links

• Crystal official site
• Crystal source code