object ErrorHandlingSection extends AnyFlatSpec with Matchers with Section
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- class TheAfterWord extends AnyRef
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Value Members
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- final def ##: Int
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- def <[T](right: T)(implicit arg0: Ordering[T]): ResultOfLessThanComparison[T]
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- def ===[T](right: Spread[T]): TripleEqualsInvocationOnSpread[T]
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- def ===(right: Null): TripleEqualsInvocation[Null]
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- def ===[T](right: T): TripleEqualsInvocation[T]
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- def >[T](right: T)(implicit arg0: Ordering[T]): ResultOfGreaterThanComparison[T]
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- def >=[T](right: T)(implicit arg0: Ordering[T]): ResultOfGreaterThanOrEqualToComparison[T]
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- def a[T](implicit arg0: ClassTag[T]): ResultOfATypeInvocation[T]
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- val a: AWord
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- val after: TheAfterWord
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- def alert: Alerter
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- def all(xs: String)(implicit collecting: Collecting[Char, String], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Char]
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- def all[K, V, JMAP[k, v] <: Map[k, v]](xs: JMAP[K, V])(implicit collecting: Collecting[Entry[K, V], JMAP[K, V]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Entry[K, V]]
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- def all[K, V, MAP[k, v] <: GenMap[k, v]](xs: MAP[K, V])(implicit collecting: Collecting[(K, V), GenTraversable[(K, V)]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[(K, V)]
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- def all[E, C[_]](xs: C[E])(implicit collecting: Collecting[E, C[E]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[E]
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- def allElementsOf[R](elements: GenTraversable[R]): ResultOfAllElementsOfApplication
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- def allOf(firstEle: Any, secondEle: Any, remainingEles: Any*)(implicit pos: Position): ResultOfAllOfApplication
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- val an: AnWord
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- macro def assert(condition: Boolean, clue: Any)(implicit prettifier: Prettifier, pos: Position): Assertion
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- def atLeast[K, V, JMAP[k, v] <: Map[k, v]](num: Int, xs: JMAP[K, V])(implicit collecting: Collecting[Entry[K, V], JMAP[K, V]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Entry[K, V]]
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- def atLeast[K, V, MAP[k, v] <: GenMap[k, v]](num: Int, xs: MAP[K, V])(implicit collecting: Collecting[(K, V), GenTraversable[(K, V)]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[(K, V)]
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- def atLeast[E, C[_]](num: Int, xs: C[E])(implicit collecting: Collecting[E, C[E]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[E]
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- def atLeastOneElementOf(elements: GenTraversable[Any]): ResultOfAtLeastOneElementOfApplication
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- def atLeastOneOf(firstEle: Any, secondEle: Any, remainingEles: Any*)(implicit pos: Position): ResultOfAtLeastOneOfApplication
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- def atMost(num: Int, xs: String)(implicit collecting: Collecting[Char, String], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Char]
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- def atMost[K, V, JMAP[k, v] <: Map[k, v]](num: Int, xs: JMAP[K, V])(implicit collecting: Collecting[Entry[K, V], JMAP[K, V]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Entry[K, V]]
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- def atMost[K, V, MAP[k, v] <: GenMap[k, v]](num: Int, xs: MAP[K, V])(implicit collecting: Collecting[(K, V), GenTraversable[(K, V)]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[(K, V)]
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- def atMost[E, C[_]](num: Int, xs: C[E])(implicit collecting: Collecting[E, C[E]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[E]
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- def atMostOneElementOf[R](elements: GenTraversable[R]): ResultOfAtMostOneElementOfApplication
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- def atMostOneOf(firstEle: Any, secondEle: Any, remainingEles: Any*)(implicit pos: Position): ResultOfAtMostOneOfApplication
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- def between(from: Int, upTo: Int, xs: String)(implicit collecting: Collecting[Char, String], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Char]
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- def between[K, V, JMAP[k, v] <: Map[k, v]](from: Int, upTo: Int, xs: JMAP[K, V])(implicit collecting: Collecting[Entry[K, V], JMAP[K, V]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Entry[K, V]]
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- def between[E, C[_]](from: Int, upTo: Int, xs: C[E])(implicit collecting: Collecting[E, C[E]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[E]
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- def cancel(cause: Throwable)(implicit pos: Position): Nothing
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- def convertEquivalenceToAToBConstraint[A, B](equivalenceOfB: Equivalence[B])(implicit ev: <:<[A, B]): CanEqual[A, B]
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- def convertEquivalenceToBToAConstraint[A, B](equivalenceOfA: Equivalence[A])(implicit ev: <:<[B, A]): CanEqual[A, B]
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- implicit def convertNumericToPlusOrMinusWrapper[T](pivot: T)(implicit arg0: Numeric[T]): PlusOrMinusWrapper[T]
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- implicit def convertSymbolToHavePropertyMatcherGenerator(symbol: Symbol)(implicit prettifier: Prettifier, pos: Position): HavePropertyMatcherGenerator
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- implicit def convertToEqualizer[T](left: T): Equalizer[T]
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- implicit def convertToInAndIgnoreMethods(resultOfStringPassedToVerb: ResultOfStringPassedToVerb): InAndIgnoreMethods
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- val determined: DeterminedWord
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- def eitherFlatMapAssert(res0: Right[String], res1: Left[String], res2: Left[String]): Unit
flatMap
behaves the same inEither
as it does inOption
, allowing us to chain operations that may also fail.flatMap
behaves the same inEither
as it does inOption
, allowing us to chain operations that may also fail. Use it to try to obtain the managers from each employee. Note that when calling ourgetManager
function, we can find two different errors in its execution: - def eitherMap2Assert(res0: Right[Boolean], res1: Right[Boolean], res2: Left[String]): Unit
In the same fashion as with
Option
s,map2
lets us combine twoEither
s using a binary function.In the same fashion as with
Option
s,map2
lets us combine twoEither
s using a binary function. Note that we will use for-comprehensions instead of a chain offlatMap
andmap
calls:def map2[EE >: E, B, C](b: Either[EE, B])(f: (A, B) => C): Either[EE, C] = for { a <- this; b1 <- b } yield f(a,b1)
In this implementation, we can't report errors on both sides. To do that, we would need a new data type that can hold a list of errors:
trait Partial[+A,+B] case class Errors[+A](get: Seq[A]) extends Partial[A,Nothing] case class Success[+B](get: B) extends Partial[Nothing,B]
This data type is really similar to Scalaz'
Validation
type.In any case, let's test
map2
on the following exercise, to find out if two employees share a department by using an specific function: - def eitherMapAssert(res0: (Either[String, Employee]) => Either[String, String]): Unit
Exercise 4.6:
The Either data type
Exercise 4.6:
As we did with
Option
, let's implement versions ofmap
,flatMap
,orElse
andmap2
onEither
that operate on theRight
value, starting withmap
:def map[B](f: A => B): Either[E, B] = this match { case Right(a) => Right(f(a)) case Left(e) => Left(e) }
In the same fashion as
Option
,map
allows us to chain operations on anEither
without worrying about the possible errors that may arise, as the chain will stop if any error occurs. Let's try it out, by improving the employee lookup function we implemented before, to useEither
instead ofOption
. Try to usemap
on theEither
type to obtain the department of each employee: - def eitherOrElseAssert(res0: Right[String], res1: Right[String], res2: Right[String]): Unit
orElse
works the same as inOption
s, returning the originalEither
when it contains aRight
, or the provided alternative in case it's aLeft
:orElse
works the same as inOption
s, returning the originalEither
when it contains aRight
, or the provided alternative in case it's aLeft
:def orElse[EE >: E, AA >: A](b: => Either[EE, AA]): Either[EE, AA] = this match { case Left(_) => b case Right(a) => Right(a) }
Let's check out how it behaves. Let's assume that everyone inside our company ends up responding to a "Mr. CEO" manager. We can provide that logic with
orElse
: - def eitherSequenceAssert(res0: Right[List[Employee]], res1: Left[String]): Unit
As for
sequence
, we can create aList
of the employees we looked up by using thelookupByNameViaEither
, and find out if we were looking for a missing person: - def eitherTraverseAssert(res0: Right[List[Employee]], res1: Left[String]): Unit
Exercise 4.7:
Exercise 4.7:
sequence
andtraverse
can also be implemented forEither
. Those functions should return the first error that can be found, if there is one.def traverse[E,A,B](es: List[A])(f: A => Either[E, B]): Either[E, List[B]] = es match { case Nil => Right(Nil) case h::t => (f(h) map2 traverse(t)(f))(_ :: _) }
def sequence[E,A](es: List[Either[E,A]]): Either[E,List[A]] = traverse(es)(x => x)
We can attempt to obtain a record of employees names by looking up a list of
Employees
: - val empty: EmptyWord
- Definition Classes
- MatcherWords
- val endWith: EndWithWord
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- final def eq(arg0: AnyRef): Boolean
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- AnyRef
- def equal(o: Null): Matcher[AnyRef]
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- def equal[T](spread: Spread[T]): Matcher[T]
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- def equal(right: Any): MatcherFactory1[Any, Equality]
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- def equals(arg0: AnyRef): Boolean
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- AnyRef → Any
- def every(xs: String)(implicit collecting: Collecting[Char, String], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Char]
- Definition Classes
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- def every[K, V, JMAP[k, v] <: Map[k, v]](xs: JMAP[K, V])(implicit collecting: Collecting[Entry[K, V], JMAP[K, V]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Entry[K, V]]
- Definition Classes
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- def every[K, V, MAP[k, v] <: Map[k, v]](xs: MAP[K, V])(implicit collecting: Collecting[(K, V), GenTraversable[(K, V)]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[(K, V)]
- Definition Classes
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- def every[E, C[_]](xs: C[E])(implicit collecting: Collecting[E, C[E]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[E]
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- def exactly(num: Int, xs: String)(implicit collecting: Collecting[Char, String], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Char]
- Definition Classes
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- def exactly[K, V, JMAP[k, v] <: Map[k, v]](num: Int, xs: JMAP[K, V])(implicit collecting: Collecting[Entry[K, V], JMAP[K, V]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Entry[K, V]]
- Definition Classes
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- def exactly[K, V, MAP[k, v] <: GenMap[k, v]](num: Int, xs: MAP[K, V])(implicit collecting: Collecting[(K, V), GenTraversable[(K, V)]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[(K, V)]
- Definition Classes
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- def exactly[E, C[_]](num: Int, xs: C[E])(implicit collecting: Collecting[E, C[E]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[E]
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- final def execute(testName: String, configMap: ConfigMap, color: Boolean, durations: Boolean, shortstacks: Boolean, fullstacks: Boolean, stats: Boolean): Unit
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- Suite
- val exist: ExistWord
- Definition Classes
- MatcherWords
- def expectedTestCount(filter: Filter): Int
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- Suite
- def fail(cause: Throwable)(implicit pos: Position): Nothing
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- def fail(message: String, cause: Throwable)(implicit pos: Position): Nothing
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- def fail(message: String)(implicit pos: Position): Nothing
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- def fail()(implicit pos: Position): Nothing
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- def finalize(): Unit
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- protected[lang]
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- Annotations
- @throws(classOf[java.lang.Throwable])
- val fullyMatch: FullyMatchWord
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- final def getClass(): Class[_ <: AnyRef]
- Definition Classes
- AnyRef → Any
- Annotations
- @native()
- def hashCode(): Int
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- AnyRef → Any
- Annotations
- @native()
- val have: HaveWord
- Definition Classes
- MatcherWords
- val ignore: IgnoreWord
- Attributes
- protected
- Definition Classes
- AnyFlatSpecLike
- def inOrder(firstEle: Any, secondEle: Any, remainingEles: Any*)(implicit pos: Position): ResultOfInOrderApplication
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- def inOrderElementsOf[R](elements: GenTraversable[R]): ResultOfInOrderElementsOfApplication
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- def inOrderOnly[T](firstEle: Any, secondEle: Any, remainingEles: Any*)(implicit pos: Position): ResultOfInOrderOnlyApplication
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- val include: IncludeWord
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- MatcherWords
- def info: Informer
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- protected
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- AnyFlatSpecLike → Informing
- def intercept[T <: AnyRef](f: => Any)(implicit classTag: ClassTag[T], pos: Position): T
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- final def isInstanceOf[T0]: Boolean
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- Any
- val it: ItWord
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- protected
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- AnyFlatSpecLike
- val key: KeyWord
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- val length: LengthWord
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- MatcherWords
- def lowPriorityTypeCheckedConstraint[A, B](implicit equivalenceOfB: Equivalence[B], ev: <:<[A, B]): CanEqual[A, B]
- Definition Classes
- TripleEquals → TripleEqualsSupport
- def markup: Documenter
- Attributes
- protected
- Definition Classes
- AnyFlatSpecLike → Documenting
- val matchPattern: MatchPatternWord
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- MatcherWords
- def message(expectedMessage: String): ResultOfMessageWordApplication
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- final def ne(arg0: AnyRef): Boolean
- Definition Classes
- AnyRef
- def nestedSuites: IndexedSeq[Suite]
- Definition Classes
- Suite
- def no(xs: String)(implicit collecting: Collecting[Char, String], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Char]
- Definition Classes
- Matchers
- def no[K, V, JMAP[k, v] <: Map[k, v]](xs: JMAP[K, V])(implicit collecting: Collecting[Entry[K, V], JMAP[K, V]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[Entry[K, V]]
- Definition Classes
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- def no[E, C[_]](xs: C[E])(implicit collecting: Collecting[E, C[E]], prettifier: Prettifier, pos: Position): ResultOfCollectedAny[E]
- Definition Classes
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- def noElementsOf(elements: GenTraversable[Any]): ResultOfNoElementsOfApplication
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- def noException(implicit pos: Position): NoExceptionWord
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- def noneOf(firstEle: Any, secondEle: Any, remainingEles: Any*)(implicit pos: Position): ResultOfNoneOfApplication
- Definition Classes
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- val not: NotWord
- Definition Classes
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- def note: Notifier
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- Definition Classes
- Matchers
- def optionFilterAssert(res0: Some[Employee], res1: Option[Employee], res2: Option[Employee]): Unit
Finally, we can implement a
filter
function that will turn anyOption
into aNone
if it doesn't satisfy the provided predicate:Finally, we can implement a
filter
function that will turn anyOption
into aNone
if it doesn't satisfy the provided predicate:def filter(f: A => Boolean): Option[A] = this match { case Some(a) if f(a) => this case _ => None }
Test it out by discarding those employees who belong to the IT department:
- def optionFlatMapAssert(res0: (Option[Employee]) => Option[String]): Unit
We can also implement
flatMap
, which applies a functionf
which may also fail, to theOption
if notNone
:We can also implement
flatMap
, which applies a functionf
which may also fail, to theOption
if notNone
:def flatMap[B](f: A => Option[B]): Option[B] = map(f) getOrElse None
Try to find out who is managing each employee, if applicable:
- def optionMapAssert(res0: (Option[Employee]) => Option[String]): Unit
The following set of sections represent the exercises contained in the book "Functional Programming in Scala", written by Paul Chiusano and Rúnar Bjarnason and published by Manning.
Functional programming in Scala
The following set of sections represent the exercises contained in the book "Functional Programming in Scala", written by Paul Chiusano and Rúnar Bjarnason and published by Manning. This content library is meant to be used in tandem with the book. We use the same numeration for the exercises for you to follow them.
For more information about "Functional Programming in Scala" please visit its official website.
The Option data type
Exercise 4.1:
We're going to look at some of the functions available in the
Option
, starting bymap
, that applies a functionf
in theOption
is notNone
:def map[B](f: A => B): Option[B] = this match { case None => None case Some(a) => Some(f(a)) }
Let's try it out:
- def optionOrElseAssert(res0: Some[String], res1: Some[String], res2: Some[String]): Unit
The function
getOrElse
tries to get the value contained in the Option, but if it's aNone
, it will return the default value provided by the caller:The function
getOrElse
tries to get the value contained in the Option, but if it's aNone
, it will return the default value provided by the caller:def getOrElse[B>:A](default: => B): B = this match { case None => default case Some(a) => a }
orElse
returns the originalOption
if notNone
, or returns the providedOption
as an alternative in that case:def orElse[B>:A](ob: => Option[B]): Option[B] = this map (Some(_)) getOrElse ob
Check how it works in the following exercise:
- def optionSequenceAssert(res0: Some[List[Int]], res1: Option[List[Int]]): Unit
Exercise 4.2:
Exercise 4.2:
Let's implement the
variance
function in terms offlatMap
. If the mean of a sequence ism
, the variance is the mean ofmath.pow(x - m, 2)
for each element in the sequence:def variance(xs: Seq[Double]): Option[Double] = mean(xs) flatMap (m => mean(xs.map(x => math.pow(x - m, 2))))
Exercise 4.3:
Let's write a generic function to combine two
Option
values , so that if any of those values isNone
, the result value is too; and otherwise it will be the result of applying the provided function:def map2[A,B,C](a: Option[A], b: Option[B])(f: (A, B) => C): Option[C] = a flatMap (aa => b map (bb => f(aa, bb)))
Exercise 4.4:
Let's continue by looking at a few other similar cases. For instance, the
sequence
function, which combines a list ofOption
s into anotherOption
containing a list of all theSome
s in the original one. If the original list containsNone
at least once, the result of the function should beNone
. If not, the result should be aSome
with a list of all the values:def sequence(a: List[Option[A]]): Option[List[A]] = a match { case Nil => Some(Nil) case h :: t => h flatMap (hh => sequence(t) map (hh :: _)) }
After taking a look at the implementation, see how it works in the following exercise:
- def optionTraverseAssert(res0: Some[List[Int]], res1: Option[List[Int]]): Unit
Exercise 4.5:
Exercise 4.5:
The last
Option
function we're going to explore istraverse
, that will allow us to map over a list using a function that might fail, returningNone
if applying it to any element of the list returnsNone
:def traverse[A, B](a: List[A])(f: A => Option[B]): Option[List[B]] = a match { case Nil => Some(Nil) case h::t => map2(f(h), traverse(t)(f))(_ :: _) }
We can also implement
traverse
in terms offoldRight
:def traverse_1[A, B](a: List[A])(f: A => Option[B]): Option[List[B]] = a.foldRight[Option[List[B]]](Some(Nil))((h,t) => map2(f(h),t)(_ :: _))
We can even re-implement
sequence
in terms oftraverse
:def sequenceViaTraverse[A](a: List[Option[A]]): Option[List[A]] = traverse(a)(x => x)
Let's try
traverse
out, by trying to parse aList[String]
into aOption[List[Int]]
: - def pending: Assertion with PendingStatement
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Deprecated Value Members
- def conversionCheckedConstraint[A, B](implicit equivalenceOfA: Equivalence[A], cnv: (B) => A): CanEqual[A, B]
- Definition Classes
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- Annotations
- @deprecated
- Deprecated
(Since version 3.1.0) The conversionCheckedConstraint method has been deprecated and will be removed in a future version of ScalaTest. It is no longer needed now that the deprecation period of ConversionCheckedTripleEquals has expired. It will not be replaced.
- def convertEquivalenceToAToBConversionConstraint[A, B](equivalenceOfB: Equivalence[B])(implicit ev: (A) => B): CanEqual[A, B]
- Definition Classes
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- Annotations
- @deprecated
- Deprecated
(Since version 3.1.0) The convertEquivalenceToAToBConversionConstraint method has been deprecated and will be removed in a future version of ScalaTest. It is no longer needed now that the deprecation period of ConversionCheckedTripleEquals has expired. It will not be replaced.
- def convertEquivalenceToBToAConversionConstraint[A, B](equivalenceOfA: Equivalence[A])(implicit ev: (B) => A): CanEqual[A, B]
- Definition Classes
- TripleEquals → TripleEqualsSupport
- Annotations
- @deprecated
- Deprecated
(Since version 3.1.0) The convertEquivalenceToBToAConversionConstraint method has been deprecated and will be removed in a future version of ScalaTest. It is no longer needed now that the deprecation period of ConversionCheckedTripleEquals has expired. It will not be replaced.
- def lowPriorityConversionCheckedConstraint[A, B](implicit equivalenceOfB: Equivalence[B], cnv: (A) => B): CanEqual[A, B]
- Definition Classes
- TripleEquals → TripleEqualsSupport
- Annotations
- @deprecated
- Deprecated
(Since version 3.1.0) The lowPriorityConversionCheckedConstraint method has been deprecated and will be removed in a future version of ScalaTest. It is no longer needed now that the deprecation period of ConversionCheckedTripleEquals has expired. It will not be replaced.
- final val styleName: String
- Definition Classes
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- Annotations
- @deprecated
- Deprecated
(Since version 3.1.0) The styleName lifecycle method has been deprecated and will be removed in a future version of ScalaTest with no replacement.