// GENERATED
/* INSTRUCTIONS
*
* Complete the exercises below. For each “EXERCISE” comment, add
* code immediately below the comment.
*
* Please see README.md for instructions, including compilation and testing.
*
* GRADING
*
* 1. Submissions MUST compile using SBT with UNCHANGED configuration and tests with no
* compilation errors. Submissions with compilation errors will receive 0 points.
* Note that refactoring the code will cause the tests to fail.
*
* 2. You MUST NOT edit the SBT configuration and tests. Altering it in your submission will
* result in 0 points for this assignment.
*
* 3. You MUST NOT use while loops or (re)assignment to variables (you can use “val” declarations,
* but not “var” declarations). You must use recursion instead.
*
* 4. You may declare auxiliary functions if you like.
*
* SUBMISSION
*
* 1. Push your local repository to the repository created for you on Bitbucket before the deadline.
*
* 2. Late submissions will not be permitted because solutions will be discussed in class.
*
*/
object subtyping {
// Instances of Counter have a integer field that can be incremented, decremented, or read.
class Counter {
private var n = 0
def increment () = { n = n + 1 }
def decrement () = { n = n – 1 }
def get () : Int = n
}
// EXERCISE 1: complete the following function.
// The observeCounter function has one parameter f: a function that accepts (a reference to) a Counter instance but returns nothing.
// The observeCounter function should call f with (a reference to) an object (of a class extending Counter).
// Your class that extends Counter must keep track of the total number of times that increment/decrement have been called.
// I.e., if the increment method is called 3 times on an instance, and the decrement method is called 2 times on the same instance, then it should store 5 (somewhere other than the existing field n).
// observeCounter should call f, and then return the total number of times that increment/decrement were called on the instance by f.
def observeCounter (f : Counter => Unit) : Int = {
val o1 = new Counter()
f(o1)
o1.get()
// TODO: Provide definition here.
// -1
}
// EXERCISE 2: complete the following function.
// It is the same as observeCounter except that f has a parameter of type List[Counter] not Counter.
// f will insist that the List[Counter] has length 3.
// You must return a List[Int] not an Int.
// The first element of the result List[Int] must correspond to the number of times that increment/decrement were called on the first element of type List[Counter], similarly for the second and third elements.
def observeCounterList (f : List[Counter] => Unit) : List[Int] = {
// TODO: Provide definition here.
List (-1, -1, -1)
}
// EXERCISE 3: complete the following function.
// It is the same as observeCounterList except that f has a parameter of type Array[Counter] not List[Counter].
// f will insist that the Array[Counter] has length 3.
// You must return a Array[Int] not a List[Int].
// The first element of the result Array[Int] must correspond to the number of times that increment/decrement were called on the first element of type Array[Counter], similarly for the second and third elements.
def observeCounterArray (f : Array[Counter] => Unit) : Array[Int] = {
// TODO: Provide definition here.
List (-1, -1, -1).toArray
}
}
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