Scalaジェネリクス（パラメータ化された型）

• クラスのジェネリクス
• メソッドのジェネリクス
• 型パラメーターの境界
• 型パラメーターの制約 [2011-07-24]
• 変位指定
• Javaで出来なかった事 [/2013-06-08]

• クラス
• オブジェクト
• トレイト

• Naotsuguさんの型パラメータの境界とは

• Javaジェネリクス

class Example[T] {
  protected var t: T = _

  def set(t: T): Unit = {
    this.t = t
  }

  def get(): T = {
    t
  }
}

public class Example<T> {
  protected T t;

  public void set(T t) {
    this.t = t;
  }

  public T get() {
    return t;
  }
}

val s = new Example[String]
        s.set("abc")
val v = s.get()

final Example<String> s = new Example<String>();
                 s.set("abc");
final String v = s.get();

def f(s:Example[_]) = println(s)

public void f(Example<?> s) {
  System.out.println(s);
}

class Example[T] extends Parent[T] {
}

public class Example<T> extends Parent<T> {
}

class Example[T, U] {
  def method1(t: T): Unit = {
    println(t)
  }
  def method2(u: U): Unit = {
    println(u)
  }
}

public class Example<T, U> {
  public void method1(T t) {
    System.out.println(t);
  }
  public void method2(U u) {
    System.out.println(u);
  }
}

val s = new Example[String, Int]

val s = new Example[String, Int]()

final Example<String, Integer> s =
  new Example<Stirng, Integer>();

val s = new (String Example Int)

val s = new (String Example Int)()

scala> class op[L, R]
defined class op

scala> class A; class B; class C
defined class A
defined class B
defined class C

scala> new (A op B)
res1: op[A,B] = op@138d2fc

scala> new (A op B op C)
res2: op[op[A,B],C] = op@d76d51

class Example {
  def method[T](t: T): T = {
    t
  }
}

public class Example {
  public <T> T method(T t) {
    return t;
  }
}

val obj = new Example
val s = obj.method("abc")

final Example obj = new Example();
final String s = obj.method("abc");

val s = obj.method[String](null)

final String s = obj.<String>method(null);

class Example[T] {
}

○ new Example[Any]
○ new Example[A1]
○ new Example[A2]
○ new Example[A3]
○ new Example[Nothing]

class Example<T> {
}

○ new Example<Object>();
○ new Example<A1>();
○ new Example<A2>();
○ new Example<A3>();

class Example[T <: A2] {
}

× new Example[Any]
× new Example[A1]
○ new Example[A2]
○ new Example[A3]
○ new Example[Nothing]

class Example<T extends A2> {
}

× new Example<Object>();
× new Example<A1>();
○ new Example<A2>();
○ new Example<A3>();

class Example[T >: A2] {
}

○ new Example[Any]
○ new Example[A1]
○ new Example[A2]
× new Example[A3]
× new Example[Nothing]

class Example[T >: A3 <: A1] {
}

× new Example[Any]
○ new Example[A1]
○ new Example[A2]
○ new Example[A3]
× new Example[Nothing]

class Example[T <% scala.runtime.RichInt] {
}

× new Example[Any]
○ new Example[scala.runtime.RichInt]
○ new Example[Int]
○ new Example[Nothing]

//上限境界では、暗黙変換は無関係
class Example[T <: scala.runtime.RichInt] {
}

× new Example[Any]
○ new Example[scala.runtime.RichInt]
× new Example[Int]
○ new Example[Nothing]

class Example[T]

def fu(s: Example[_ <: A2]) = println(s)
× fu(new Example[Any])
× fu(new Example[A1])
○ fu(new Example[A2])
○ fu(new Example[A3])
○ fu(new Example[Nothing])

def fl(s: Example[_ >: A2]) = println(s)
○ fl(new Example[Any])
○ fl(new Example[A1])
○ fl(new Example[A2])
× fl(new Example[A3])
× fl(new Example[Nothing])

def fb(s: Example[_ >: A3 <: A1]) = println(s)
× fb(new Example[Any])
○ fb(new Example[A1])
○ fb(new Example[A2])
○ fb(new Example[A3])
× fb(new Example[Nothing])

class Example<T> {}

public void fu(Example<? extends A2> s) {
  System.out.println(s);
}

public void fl(Example<? super A2> s) {
  System.out.println(s);
}

import java.io._

class Example[T <: Serializable with Closeable] {
}

class SC extends Serializable with Closeable {


  def close() = {}
}

new Example[SC]

import java.io.*;

class Example<T extends Serializable & Closeable> {
}

class SC implements Serializable, Closeable {

  @Override
  public void close() throws IOException {}
}

new Example<SC>();

class Example[T <: { def close():Unit }] {
}

class Example[T : Hoge] {
}

class MyList[T] {
}

var list:MyList[A2] = _

× list = new MyList[A1]
○ list = new MyList[A2]
× list = new MyList[A3]

class MyList<T> {
}

MyList<A2> list = null;

× list = new MyList<A1>();
○ list = new MyList<A2>();
× list = new MyList<A3>();

List<String> list = new ArrayList<String>();

class MyArray[+T] {
}

var array:MyArray[A2] = _

× array = new MyArray[A1]
○ array = new MyArray[A2]
○ array = new MyArray[A3]

A2[] array = null;

× array = new A1[] {};
○ array = new A2[] {};
○ array = new A3[] {};

Object[] array = new String[] {};

class MyList[-T] {
}

var list:MyList[A2] = _

○ list = new MyList[A1]
○ list = new MyList[A2]
× list = new MyList[A3]

//×出来ない（コンパイルエラー）
class Example[T] {
  def printClass(): Unit = {
    val c = classOf[T]
    println(c)
  }
}

//×出来ない（コンパイルエラー）
public class Example<T> {
  public void printClass() {
    final Class c = T.class;
    System.out.println(c);
  }
}

class Example[T](implicit m: ClassTag[T]) {
  def printClass(): Unit = {
    val c = m.runtimeClass
    println(c)
  }
}

val s = new Example[String]
s.printClass()

//×出来ない（コンパイルエラー）
class Example[T] {
  def create(): T = {
    new T()
  }
}

//×出来ない（コンパイルエラー）
public class Example<T> {
  public T create() {
    return new T();
  }
}

class Example[T](implicit m: ClassTag[T]) {
  def create(): T = {
    m.runtimeClass.newInstance().asInstanceOf[T]
  }
}

val s = new Example[String]
val v = s.create()

class Example[T](implicit m: ClassTag[T]) {
  def create(size:Int): Array[T] = {
    m.newArray(size)
  }
}

val s = new Example[Int]
val a = s.create(10)

//×出来ない（コンパイルエラー）
public class Example<T> {
  public T[] create(int size) {
    return new T[size];
  }
}

//×コンパイルは通るが、正しく動作しない
class Example[T] {
  def check(o:AnyRef): Boolean = {
    o.isInstanceOf[T]
  }
}

//×出来ない（コンパイルエラー）
public class Example<T> {
  public boolean check(Object o) {
    return (o instanceof T);
  }
}

  def check(o:AnyRef): Boolean = o match {
    case _:T => true
    case _   => false
  }

class Example[T](implicit m: ClassTag[T]) {
  def check(o:AnyRef): Boolean = {
    (o ne null) && m.runtimeClass.isInstance(o)
  }
}

val d = new Example[java.util.Date]
assert( d.check(new java.util.Date()) )
assert( d.check(new java.sql.Date(0)) )
assert(!d.check("abc") )
assert(!d.check(null) )

val q = new Example[java.sql.Date]
assert( q.check(new java.sql.Date(0)) )
assert(!q.check(new java.util.Date()) )

class Example[T](implicit m: ClassTag[T]) {
  def check[S](o:S)(implicit s: ClassTag[S]): Boolean = {
    m.runtimeClass.isAssignableFrom(s.runtimeClass)
  }
}

//×出来ない（コンパイルエラー）
public class Example<T> {
  private static T value;
}