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# sk-spr's solution

## to Accumulate in the Swift Track

Published at Feb 05 2021 · 0 comments
Instructions
Test suite
Solution

Implement the `accumulate` operation, which, given a collection and an operation to perform on each element of the collection, returns a new collection containing the result of applying that operation to each element of the input collection.

Given the collection of numbers:

• 1, 2, 3, 4, 5

And the operation:

• square a number (`x => x * x`)

Your code should be able to produce the collection of squares:

• 1, 4, 9, 16, 25

Check out the test suite to see the expected function signature.

## Restrictions

Keep your hands off that collect/map/fmap/whatchamacallit functionality provided by your standard library! Solve this one yourself using other basic tools instead.

## Setup

Go through the project setup instructions for Xcode using Swift:

http://exercism.io/languages/swift
http://exercism.io/languages/swift/tests

Notably from the source directory:

`swift test` runs tests
`swift package generate-xcodeproj` creates an Xcode project

## Source

Conversation with James Edward Gray II https://twitter.com/jeg2

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### AccumulateTests.swift

``````import XCTest
@testable import Accumulate

private extension String {
var length: Int { return self.count }

func reverse() -> String {
var result: String = ""
for char in self {
result = "\(char)\(result)"
}
return result
}
}

private extension XCTest {
func XCTAssertEqualMultiArray(_ aArray1: [[String]], _ aArray2: [[String]]) {
XCTAssertEqual(Array(aArray1.joined()), Array(aArray2.joined()))
}
}

class AccumulateTests: XCTestCase {
func testEmptyAccumulation() {
let input = [Int]()
func square(_ input: Int) -> Int {
return input * input
}
let result = input.accumulate(square)

XCTAssertTrue(result.isEmpty)
}

func testAccumulateSquares() {
let input = [1, 2, 3, 4]
let expected = [1, 4, 9, 16]
func square(_ input: Int) -> Int {
return input * input
}
let result = input.accumulate(square)

XCTAssertEqual(expected, result)
}

func testAccumulateUpcases() {
let input = ["hello", "world"]
let expected = ["HELLO", "WORLD"]
func toUpper(_ input: String) -> String {
return input.uppercased()
}
let result = input.accumulate(toUpper)

XCTAssertEqual(expected, result)

}

func testAccumulateReversedStrings() {
let input =    ["the", "quick", "brown", "fox", "etc"]
let expected = ["eht", "kciuq", "nworb", "xof", "cte"]
func reverse(_ input: String) -> String {
return input.reverse()
}
let result = input.accumulate(reverse)

XCTAssertEqual(expected, result)
}

func testAccumulateRecursively() {
let input =   ["a", "b", "c"]
let expected = [
["a1", "a2", "a3"],
["b1", "b2", "b3"],
["c1", "c2", "c3"]
]
func recurse(_ input: String) -> [String] {
func appendTo(_ innerInput: String) -> String {
return input+innerInput
}
let result = ["1", "2", "3"].accumulate(appendTo)
return result
}
let result = input.accumulate(recurse)

XCTAssertEqualMultiArray(expected, result)
}

static var allTests: [(String, (AccumulateTests) -> () throws -> Void)] {
return [
("testEmptyAccumulation", testEmptyAccumulation),
("testAccumulateSquares", testAccumulateSquares),
("testAccumulateUpcases", testAccumulateUpcases),
("testAccumulateReversedStrings", testAccumulateReversedStrings),
("testAccumulateRecursively", testAccumulateRecursively),
]
}
}``````

### LinuxMain.swift

``````import XCTest
@testable import AccumulateTests

XCTMain([
testCase(AccumulateTests.allTests),
])``````
``````public extension Array{
func accumulate(_ function: (Element)->Element)->[Element]{
var out = [Element]()
for item in self{
out += [function(item)]
}
return out
}
func accumulate(_ function: (Element)->[Element])->[[Element]]{
var out = [[Element]]()
for item in self {
out += [function(item)]
}
return out
}
}``````

### What can you learn from this solution?

A huge amount can be learned from reading other peopleâ€™s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

• What compromises have been made?