Scala

大纲

Scala是什么

语法（特色）

类库和工具

缺点

"Which Programming Language would you use *now*
on top of JVM, except Java?". The answer was
surprisingly fast and very clear: - Scala.

http://www.adam-bien.com/roller/abien/entry/java_net_javaone_which_programming

I can honestly say if someone had shown me
theProgramming in Scala book by by Martin
Odersky, Lex Spoon & Bill Venners back in 2003 I'd
probably have never created Groovy.

http://macstrac.blogspot.com/2009/04/scala-as-long-term-replacement-for.html

Scala是……

又一个JVM上的语言（编译）

Scala是……


强类型

Scala是……


强类型

“动态的”静态语言

Scala是……


强类型


函数式

Scala是……


强类型


函数式

面向对象

谁在用

Twitter

LinkedIn

FourSquare

Xerox、Sony、Siemens

Hello world!

object Test {
! def main(args: Array[String]) {
! ! println("Hello, world!")
! }
}

Hello world!

没有分号
object Test {
! }
}

Hello world!

没有分号
object Test {
定义后置
! }
}

Hello world!

没有分号
object Test {
定义后置
object ! }
}

Hello world!

没有分号
object Test {
定义后置
object ! }
}
def

Hello world!

没有分号
object Test {
定义后置
object ! }
}
def

println

Hello world!
object Test extends Application {
! println("Hello, world！")
}

Hello world!

extends
}

Hello world!

extends
}

类内直接写代码

简化
val i = 1.2.toInt
val list = List(1, 2, 3)

简化
val i = 1.2.toInt

val map = Map("Guangzhou" -> "GZ",
"Shenzhen" -> "SZ")

简化
val i = 1.2.toInt

"Shenzhen" -> "SZ")
class MyClass(x: Int, y: Int) {}

简化
val i = 1.2.toInt

"Shenzhen" -> "SZ")
list.exists(_ == 2) //true

简化
val i = 1.2.toInt

"Shenzhen" -> "SZ")
list.exists(_ == 2) //true
val (a, b, _) = (x, y, z)

函数式编程

list.ﬁlter(e => e % 2 == 0)

函数式编程


list.ﬁlter(_ % 2 == 0)

函数式编程


list.ﬁlter(_ % 2 == 0)

val f = (e: Int) => e % 2 == 0

list.ﬁlter(f)

open class(ruby)
class String
def foo
"foo"
end
end
puts "".foo # prints "foo"

为什么我们需要open class


StringUtils.isBlank("some str")



"some str".isBlank



"some str".isBlank

myObj should not contains(13)

隐式转换
class MyString(str: String) {
def isBlank = str.trim.length == 0
}
implicit def myStringWrapper(str: String) = new
MyString(str)

println("some str".isBlank)

隐式转换
class MyString(str: String) {
def isBlank = str.trim.length == 0
}
implicit def myStringWrapper(str: String) = new
MyString(str)

println("some str".isBlank)

println(new MyString("some str").isBlank)

open class的效果让大家觉得Scala是动态语言，但选择
隐式转换来实现，正好证明了Scala是静态语言

Trait
class Animal { xxx }
trait CanFly {
def ﬂy {
println("ﬂy")
}
}
class Bird extends Animal
with CanFly {}

Trait
class Animal { xxx }
trait CanFly {
Mixin，类似多集成 def ﬂy {
println("ﬂy")
接口和实现一起出现 }
}
是什么和拥有什么功能
class Bird extends Animal
with CanFly {}

Trait
class Fish { xxx }
trait CanFly {
def fly {
println("fly")
}
}
val flyFish = new Fish with CanFly

Actors
val myActor = actor {
loop {
react {
case "Send" => {
println("Get")
}
}
}
}
myActor ! "Send"

模式匹配
def matchTest(x: Any) = x match {
case 1 => "number one"
case y: Int if y > 0 => y + 1
case head :: tail => tail
case Send(a, _) => a
case ("Send", _, b: String) => b
case _ => x
}

XML支持

println(<date>{new java.util.Date()}</date>)

是什么让我们觉得一个语言是并发的语言

是什么让我们觉得Go和Erlang是并发语
言，而C++和Python不是

是什么让我们觉得Go和Erlang是并发语
言，而C++和Python不是

Go内置Channel和Goroutine

Erlang的一次赋值、轻量级进程

是什么让我们觉得Scala

val

case class

模式匹配

大量的immutable类

Actors

与Java互相调用

Scala能调用绝大部分的Java

JavaConverters、JavaConversions

Java调用Scala独有的东西比较困难

Lift

full stack

view ﬁrst

Play!

Play Scala

Play 2.0 !!

Akka

STM & Transactors

Fault-tolerance

Transparent Remoting

Scala & Java API

更多

Xitrum

Scalatra、Scalate

ScalaTest、specs2

Squeryl

It took about 15 hours to recreate the publishing
daemon in Clojure and get it to pass all our tests.
Today we ran a "soak test" publishing nearly
300,000 proﬁles in one run. The Scala code would
fail with OoM exceptions if we hit it with 50,000
proﬁles in one run (sometimes less).

http://groups.google.com/group/clojure/browse_thread/thread/b18f9006c068f0a0

The e-mail conﬁrms that Yammer is moving its basic
infrastructure stack from Scala back to Java, owing
to issues with complexity and performance.

http://www.infoq.com/news/2011/11/yammer-scala

ﬂatMap [B, That] (f: (A) Traversable[B])(implicit bf:
CanBuildFrom[List[A], B, That]) : That

http://goodstuff.im/yes-virginia-scala-is-hard

jetbrains出了新JVM语言Kotlin后，Scala社区终于始
正视Scala太杂的问题了

http://groups.google.com/group/scalacn/browse_thread/thread/cbbe5997009db919

缺点

编译速度

二进制不兼容

语法越来越杂

太少人使用，招聘发人员的问题

始使用

使用最新版(2.9.1)

始使用


先用高级特性

始使用


先用高级特性

小工具、单元测试

始使用


先用高级特性


Java/Scala混合项目，逐步移

始使用


先用高级特性


Java/Scala混合项目，逐步移

sbt

谢谢

weibo&twitter: @sparklezeng

email: popeast@gmail.com

website: http://weavesky.com

Scala

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