企业支持
雇用我们参与您的项目
84codes 
Manas.Tech 
84codes LavinMQ：理解代码以获得最佳性能 新闻
顶级赞助商
# A very basic HTTP server
require "http/server"
server = HTTP::Server.new do |context|
context.response.content_type = "text/plain"
context.response.print "Hello world, got #{context.request.path}!"
end
address = server.bind_tcp(8080)
puts "Listening on http://#{address}"
# This call blocks until the process is terminated
server.listen
Crystal 是静态类型语言，类型错误在编译时被捕获，消除了运行时一系列类型相关的错误。
由于强大的类型推断，类型注释很少需要。这保持了代码的简洁，感觉就像动态语言一样。
def shout(x)
# Notice that both Int32 and String respond_to `to_s`
x.to_s.upcase
end
# If `ENV["FOO"]` is defined, use that, else `10`
foo = ENV["FOO"]? || 10
puts typeof(foo) # => (Int32 | String)
puts typeof(shout(foo)) # => String
nil 值由一个特殊类型表示，Nil，任何可能为 nil 的值都具有包含 Nil 的联合类型。
因此，编译器可以在编译时判断值是否为空。它强制执行对 nil 值的显式处理，有助于防止可怕的 十亿美元错误。
foo = [nil, "hello world"].sample
# The type of `foo` is a union of `String` and `Nil``
puts typeof(foo) # => String | Nil
# This would be a type error:
# puts foo.upcase # Error: undefined method 'upcase' for Nil
# The condition excludes `Nil` and inside the branch `foo`'s type is `String`.
if foo
puts typeof(foo) # => String
puts foo.upcase
end
class String
def longest_repetition?
max = chars
.chunk(&.itself)
.map(&.last)
.max_by?(&.size)
{max[0], max.size} if max
end
end
puts "aaabb".longest_repetition? # => {'a', 3}
channel = Channel(Int32).new
3.times do |i|
spawn do
3.times do |j|
sleep rand(100).milliseconds # add non-determinism for fun
channel.send 10 * (i + 1) + j
end
end
end
9.times do
puts channel.receive
end
# Define the lib bindings and link info:
@[Link("m")]
lib LibM
fun pow(x : LibC::Double, y : LibC::Double) : LibC::Double
end
# Call a C function like a Crystal method:
puts LibM.pow(2.0, 4.0) # => 16.0
# This example intentionally uses a simple standard C function to be succinct.
# Of course you could do *this specific* calculation in native Crystal as well:
# 2.0 ** 4.0 # => 16.0
class Object
def has_instance_var?(name) : Bool
{{ @type.instance_vars.map &.name.stringify }}.includes? name
end
end
class Person
property name : String
def initialize(@name)
end
end
person = Person.new "John"
p! person.has_instance_var?("name") # => true
p! person.has_instance_var?("birthday") # => false
Crystal 库打包成 Shards，这是一个没有集中式仓库的分布式依赖管理工具。
它读取 shard.yml 中定义的依赖关系，并从它们的仓库中获取源代码。
name: my-first-crystal-app
version: 1.0.0
license: Apache-2.0
authors:
- Crys <[email protected]>
dependencies:
mysql:
github: crystal-lang/crystal-mysql
version: ~>0.16.0
development_dependencies:
ameba:
github: crystal-ameba/ameba
