Odersky week1 notes
Download as PPT, PDF0 likes312 views
This document discusses function types in Scala, including defining functions as objects or classes that extend function types. It provides examples of defining a factorial function recursively and using function types, as well as discussing recursion patterns like base cases and inductive steps. It also briefly mentions fold operations like foldLeft and foldRight, and using for comprehensions as a substitute for map/flatMap/filter operations.
![Function Types
Denoted as Int=>Int or type a = Int=>Int, not
just a mapping but an apply to each element
Abstract, they need an implementation
import scala.reflect.runtime.universe._
- Scala 2.10+; failed in 2.9.3 didnt debug
typeOf[a] and typeOf[a].members
- scala> typeOf[test].members
- res16: reflect.runtime.universe.MemberScope = Scopes(method apply,
constructor test, method toString, method andThen, method compose, method
$init$, method $asInstanceOf, method $isInstanceOf, method synchronized,
method ##, method !=, method ==, method ne, method eq, method notifyAll,
method notify, method clone, method getClass, method hashCode, method
equals, method wait, method wait, method wait, method finalize, method
asInstanceOf, method isInstanceOf)](https://image.slidesharecdn.com/oderskyweek1-140928183035-phpapp01/85/Odersky-week1-notes-2-320.jpg)
![FunctionTypes
Function Type example
- Int=>Int same as
new Function1[Int, Int] {
- def apply(x: Int): Int = x
- }
apply default method for anon class Function1, maps
int input to int output, can add transformations to
types
- can override the apply function](https://image.slidesharecdn.com/oderskyweek1-140928183035-phpapp01/85/Odersky-week1-notes-4-320.jpg)
![Scala Classes
Employee[T], Employee[+T], Employee[-T]](https://image.slidesharecdn.com/oderskyweek1-140928183035-phpapp01/85/Odersky-week1-notes-12-320.jpg)
Odersky week1 notes
- 1. Odersky Scala Week 1 Function Types(goal to design APIs) Recursion inside an API Recursion base case + inductive step FoldLeft/FoldRight
- 2. Function Types Denoted as Int=>Int or type a = Int=>Int, not just a mapping but an apply to each element Abstract, they need an implementation import scala.reflect.runtime.universe._ - Scala 2.10+; failed in 2.9.3 didnt debug typeOf[a] and typeOf[a].members - scala> typeOf[test].members - res16: reflect.runtime.universe.MemberScope = Scopes(method apply, constructor test, method toString, method andThen, method compose, method $init$, method $asInstanceOf, method $isInstanceOf, method synchronized, method ##, method !=, method ==, method ne, method eq, method notifyAll, method notify, method clone, method getClass, method hashCode, method equals, method wait, method wait, method wait, method finalize, method asInstanceOf, method isInstanceOf)
- 3. Reference for slide before scala> object test extends (Int=>Int){ | override def apply(x:Int)={ | x+10 | } | } defined object test
- 4. FunctionTypes Function Type example - Int=>Int same as new Function1[Int, Int] { - def apply(x: Int): Int = x - } apply default method for anon class Function1, maps int input to int output, can add transformations to types - can override the apply function
- 5. Apply example, modify to add 10 scala> object test extends (Int=>Int){ | override def apply(x:Int)={ | x+10 | } | } defined object test scala> test(1) res5: Int = 11
- 6. Objects vs Classes Objects implement a function type signature scala> class test extends (Int=>Int){ | override def apply(x:Int)={ | x+10 | } | } defined class test scala> val t = new test t: test = <function1> scala> test(1) res6: Int = 11
- 7. Factorial Factorial using functional part of Scala scala> object factorial extends(Int=>Int){ def apply(x:Int):Int={ x*(if(x>1) apply(x-1) else x) } } defined object factorial scala> factorial(3) res4: Int = 6 Use scala to define your API, either a singleton or class for others to use
- 8. Recursion Base case and inductive step Tail Recursion Recursion uses result of first step in next step. - Finding max/min requires looking at each element - Uses reduce - Fold is like reduce but has initial value Scala collection operations - Reduce, foldLeft, foldRight implement TR - Not always easy to understand
- 9. Factorial scala> def factorial(x:Int) = (1 to x).reduce(_*_) factorial: (x: Int)Int scala> factorial(3) res1: Int = 6
- 10. For comprehension Not a for loop - For comprehension not a for loop as in Java, is a substitute for map/flatMap/filter - Reduce/Fold+For comprehension together
- 11. Maven + Scalacheck Add Maven Add Scalatest/Scalacheck
- 12. Scala Classes Employee[T], Employee[+T], Employee[-T]
- 13. Scala Method type bounds