Präsentation bei der Scala User Group über Type Classes in Scala.

1. TYPE CLASSES
Ad-Hoc Polymorphismus ohne Unterklassen
Scala User Group Köln/Bonn
@scalacgn
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2. POLYMORPHISMUS
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3. POLYMORPHISMUS
• Parametrisiert
• Generische Funktionen und Datentypen
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4. POLYMORPHISMUS
• Parametrisiert
• Generische Funktionen und Datentypen
• Ad-hoc
• Methoden- und Operator-Overloading
• Unterklassen (Subtype Polymorphismus)
• Type Classes
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5. CASE CLASSES SERIALISIEREN
package model {
case class Person(firstName: String, lastName: String)
case class Restaurant(name: String, address: String)
}
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6. CASE CLASSES SERIALISIEREN
package model {
case class Person(firstName: String, lastName: String)
case class Restaurant(name: String, address: String)
}
Neue
JSON CSV XML
Funktion
Person toJson toCsv toXml
Restaurant toJson toCsv toXml
Neuer Typ
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7. ÜBERLADEN
1. object JsonSerializer {
2. def toJson(person: Person): String = """{ name : "%s %s" }""".format(person.firstName, person.lastName)
3. def toJson(r: Restaurant) = """{ name : "%s"; address: "%s" }""".format(r.name, r.address)
4. }
5.
6. object CsvSerializer {
7. def toCSV(person: Person): String = "%s,%s".format(person.firstName, person.lastName)
8. def toCSV(r: Restaurant): String = "%s,%s".format(r.name, r.address)
9. }
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8. ÜBERLADEN
1. object JsonSerializer {
2. def toJson(person: Person): String = """{ name : "%s %s" }""".format(person.firstName, person.lastName)
3. def toJson(r: Restaurant) = """{ name : "%s"; address: "%s" }""".format(r.name, r.address)
4. }
5.
6. object CsvSerializer {
7. def toCSV(person: Person): String = "%s,%s".format(person.firstName, person.lastName)
8. def toCSV(r: Restaurant): String = "%s,%s".format(r.name, r.address)
9. }
+Einfach
- Kein Zusammenhang außer Methodenname
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9. UNTERKLASSEN
1. abstract class Serializer {
2. def toJson: String
3. def toCSV: String
4. }
5.
6. case class Person(firstName: String, lastName: String) extends Serializer {
7. override def toJson: String = """{ name : "%s %s" }""".format(firstName, lastName)
8. override def toCSV: String = "%s,%s".format(firstName, lastName)
9. }
10.
11. case class Restaurant(name: String, address: String) extends Serializer {
12. override def toJson(r: Restaurant) = """{ name : "%s"; address: "%s" }""".format(r.name, r.address)
13. override def toCSV(r: Restaurant): String = "%s,%s".format(r.name, r.address)
14. }
1. import models._
2. Person("Max", "Mustermann").toJson
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10. UNTERKLASSEN
1. abstract class Serializer {
2. def toJson: String
3. def toCSV: String
4. }
5.
6. case class Person(firstName: String, lastName: String) extends Serializer {
7. override def toJson: String = """{ name : "%s %s" }""".format(firstName, lastName)
8. override def toCSV: String = "%s,%s".format(firstName, lastName)
9. }
10.
11. case class Restaurant(name: String, address: String) extends Serializer {
12. override def toJson(r: Restaurant) = """{ name : "%s"; address: "%s" }""".format(r.name, r.address)
13. override def toCSV(r: Restaurant): String = "%s,%s".format(r.name, r.address)
14. }
1. import models._
2. Person("Max", "Mustermann").toJson
+ Einfach neue Klassen hinzuzufügen
- Modellklassen müssen von Serializer ableiten
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11. TRAITS
1. trait JsonSerializer {
2. def toJson: String
3. }
4.
5. trait CsvSerializer {
6. def toCSV: String
7. }
8.
9. case class Person(firstName: String, lastName: String) extends JsonSerializer with CsvSerializer {
10. override def toJson: String = """{ name : "%s %s" }""".format(firstName, lastName)
11. override def toCSV: String = "%s,%s".format(firstName, lastName)
12. }
13.
14. case class Restaurant(name: String, address: String) extends JsonSerializer with CsvSerializer {
15. override def toJson(r: Restaurant) = """{ name : "%s"; address: "%s" }""".format(r.name, r.address)
16. override def toCSV(r: Restaurant): String = "%s,%s".format(r.name, r.address)
17. }
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12. TRAITS
1. trait JsonSerializer {
2. def toJson: String
3. }
4.
5. trait CsvSerializer {
6. def toCSV: String
7. }
8.
9. case class Person(firstName: String, lastName: String) extends JsonSerializer with CsvSerializer {
10. override def toJson: String = """{ name : "%s %s" }""".format(firstName, lastName)
11. override def toCSV: String = "%s,%s".format(firstName, lastName)
12. }
13.
14. case class Restaurant(name: String, address: String) extends JsonSerializer with CsvSerializer {
15. override def toJson(r: Restaurant) = """{ name : "%s"; address: "%s" }""".format(r.name, r.address)
16. override def toCSV(r: Restaurant): String = "%s,%s".format(r.name, r.address)
17. }
- Serialisieren hat nichts mit der Logik zu tun,
Code steht nicht immer zur Verfügung
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13. TYPE CASING
1. object JsonSerializer {
2. def toJson(x: AnyRef): String = x match {
3. case person: Person => """{ name : "%s %s" }""".format(person.firstName, person.lastName)
4. case r: Restaurant => """{ name : "%s"; address: "%s" }""".format(r.name, r.address)
5. }
6.
7. object CsvSerializer {
8. def toCSV(x: AnyRef): String = x match {
9. case person: Person => "%s,%s".format(person.firstName, person.lastName)
10. case r: Restaurant => "%s,%s".format(r.name, r.address)
11. }
12. }
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14. TYPE CASING
1. object JsonSerializer {
2. def toJson(x: AnyRef): String = x match {
3. case person: Person => """{ name : "%s %s" }""".format(person.firstName, person.lastName)
4. case r: Restaurant => """{ name : "%s"; address: "%s" }""".format(r.name, r.address)
5. }
6.
7. object CsvSerializer {
8. def toCSV(x: AnyRef): String = x match {
9. case person: Person => "%s,%s".format(person.firstName, person.lastName)
10. case r: Restaurant => "%s,%s".format(r.name, r.address)
11. }
12. }
+ Einfach neue Funktionen hinzuzufügen
- Viele Eingriffe bei neuem Typ
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15. TYPE CLASSES (1)
1. package serializer
2.
3. trait CsvSerializable[T] {
4. def toCsv(t: T): String
5. }
6.
7. object CsvSerializable {
8. import models._
9.
10. def toCsv[T](t: T)(implicit serializer: CsvSerializable[T]): String =
11. serializer.toCsv(t)
12.
13. implicit object UserSerializable extends CsvSerializable[Person] {
14. def toCsv(person: User) String =
15. "%s,%s".format(person.firstName, person.lastName)
16. }
17. }
1. import serializer._
2. val user = User(name = "Max Musterbro")
3. val csvHelper = implicitly[CsvSerializable[User]]
4. csvHelper.toCsv(user)
5.
6. // Oder
7. import serializer.CsvSerializable._
8. toCsv(User(name = "Max Musterbro"))
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16. TYPE CLASSES (2)
1. trait JsonSerializable[T] {
2. def toJson(t: T): String
3. }
4.
5. object JsonSerializable {
6. import models._
7.
8. implicit object UserSerializable extends JsonSerializable[Person] {
9. def toJson(person: Person): String =
10. """{ name : "%s", status: "%s" }""".format(person.firstName, person.lastName)
11. }
12.
13. class UserSerializer(p: Person) {
14. def toJson: String = UserSerializable.toJson(p)
15. }
16.
17. implicit def UserToSerializer(p: Person) = new UserSerializer(p)
1. import serializer.JsonSerializable._
2. User(name = "Max Musterbro").toJson
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17. TYPE CLASSES (3)
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18. TYPE CLASSES (3)
• Definition
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19. TYPE CLASSES (3)
• Definition
• Trait mit Parameter
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20. TYPE CLASSES (3)
• Definition
• Trait mit Parameter
• Companion Object mit Default Implementationen
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21. TYPE CLASSES (3)
• Definition
• Trait mit Parameter
• Companion Object mit Default Implementationen
• Beispiele in Scala: scala.math.Ordering und scala.math.Numeric
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22. TYPE CLASSES (3)
• Definition
• Trait mit Parameter
• Companion Object mit Default Implementationen
• Beispiele in Scala: scala.math.Ordering und scala.math.Numeric
•+ Gut erweiterbar
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23. TYPE CLASSES (3)
• Definition
• Trait mit Parameter
• Companion Object mit Default Implementationen
• Beispiele in Scala: scala.math.Ordering und scala.math.Numeric
•+ Gut erweiterbar
• - Viel Code, implicits manchmal undurchsichtig
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24. > CODE
• https://twitter.com/scalacgn
• http://xing.to/scala
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