trait IsIterable[Repr] extends IsIterableOnce[Repr]
A trait which can be used to avoid code duplication when defining extension
methods that should be applicable both to existing Scala collections (i.e.,
types extending Iterable) as well as other (potentially user-defined)
types that could be converted to a Scala collection type. This trait
makes it possible to treat Scala collections and types that can be implicitly
converted to a collection type uniformly. For example, one can provide
extension methods that work both on collection types and on Strings (Strings
do not extend Iterable, but can be converted to Iterable)
IsIterable provides three members:
- type member
A, which represents the element type of the targetIterable[A] - type member
C, which represents the type returned by transformation operations that preserve the collection’s elements type - method
apply, which provides a way to convert between the type we wish to add extension methods to,Repr, andIterableOps[A, Iterable, C].
Usage
One must provide IsIterable as an implicit parameter type of an implicit
conversion. Its usage is shown below. Our objective in the following example
is to provide a generic extension method mapReduce to any type that extends
or can be converted to Iterable. In our example, this includes
String.
import scala.collection.{Iterable, IterableOps} import scala.collection.generic.IsIterable class ExtensionMethods[Repr, I <: IsIterable[Repr]](coll: Repr, it: I) { def mapReduce[B](mapper: it.A => B)(reducer: (B, B) => B): B = { val iter = it(coll).iterator var res = mapper(iter.next()) while (iter.hasNext) res = reducer(res, mapper(iter.next())) res } } implicit def withExtensions[Repr](coll: Repr)(implicit it: IsIterable[Repr]): ExtensionMethods[Repr, it.type] = new ExtensionMethods(coll, it) // See it in action! List(1, 2, 3).mapReduce(_ * 2)(_ + _) // res0: Int = 12 "Yeah, well, you know, that's just, like, your opinion, man.".mapReduce(x => 1)(_ + _) // res1: Int = 59
Here, we begin by creating a class ExtensionMethods which contains our
mapReduce extension method.
Note that ExtensionMethods takes a constructor argument coll of type Repr, where
Repr represents (typically) the collection type, and an argument it of a subtype of IsIterable[Repr].
The body of the method starts by converting the coll argument to an IterableOps in order to
call the iterator method on it.
The remaining of the implementation is straightforward.
The withExtensions implicit conversion makes the mapReduce operation available
on any type Repr for which it exists an implicit IsIterable[Repr] instance.
Note how we keep track of the precise type of the implicit it argument by using the
it.type singleton type, rather than the wider IsIterable[Repr] type. We do that
so that the information carried by the type members A and C of the it argument
is not lost.
When the mapReduce method is called on some type of which it is not
a member, implicit search is triggered. Because implicit conversion
withExtensions is generic, it will be applied as long as an implicit
value of type IsIterable[Repr] can be found. Given that the
IsIterable companion object contains implicit members that return values of type
IsIterable, this requirement is typically satisfied, and the chain
of interactions described in the previous paragraph is set into action.
(See the IsIterable companion object, which contains a precise
specification of the available implicits.)
Note: Currently, it's not possible to combine the implicit conversion and the class with the extension methods into an implicit class due to limitations of type inference.
Implementing IsIterable for New Types
One must simply provide an implicit value of type IsIterable
specific to the new type, or an implicit conversion which returns an
instance of IsIterable specific to the new type.
Below is an example of an implementation of the IsIterable trait
where the Repr type is Range.
implicit val rangeRepr: IsIterable[Range] { type A = Int; type C = IndexedSeq[Int] } = new IsIterable[Range] { type A = Int type C = IndexedSeq[Int] def apply(coll: Range): IterableOps[Int, IndexedSeq, IndexedSeq[Int]] = coll }
(Note that in practice the IsIterable[Range] instance is already provided by
the standard library, and it is defined as an IsSeq[Range] instance)
- Source
- IsIterable.scala
- Alphabetic
- By Inheritance
- IsIterable
- IsIterableOnce
- AnyRef
- Any
- by any2stringadd
- by StringFormat
- by Ensuring
- by ArrowAssoc
- Hide All
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- Public
- Protected
Type Members
- abstract type A
The type of elements we can traverse over (e.g.
The type of elements we can traverse over (e.g.
Int).- Definition Classes
- IsIterableOnce
- abstract type C
The type returned by transformation operations that preserve the same elements type (e.g.
The type returned by transformation operations that preserve the same elements type (e.g.
filter,take).In practice, this type is often
Repritself, excepted in the case ofSeqView[A](and otherView[A]subclasses), where it is “only”View[A].
Abstract Value Members
- abstract def apply(coll: Repr): IterableOps[A, Iterable, C]
A conversion from the type
ReprtoIterableOps[A, Iterable, C]A conversion from the type
ReprtoIterableOps[A, Iterable, C]- Definition Classes
- IsIterable → IsIterableOnce
Concrete Value Members
- final def !=(arg0: Any): Boolean
Test two objects for inequality.
Test two objects for inequality.
- returns
trueif !(this == that), false otherwise.
- Definition Classes
- AnyRef → Any
- final def ##: Int
Equivalent to
x.hashCodeexcept for boxed numeric types andnull.Equivalent to
x.hashCodeexcept for boxed numeric types andnull. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. Fornullreturns a hashcode wherenull.hashCodethrows aNullPointerException.- returns
a hash value consistent with ==
- Definition Classes
- AnyRef → Any
- def +(other: String): String
- Implicit
- This member is added by an implicit conversion from IsIterable[Repr] toany2stringadd[IsIterable[Repr]] performed by method any2stringadd in scala.Predef.
- Definition Classes
- any2stringadd
- def ->[B](y: B): (IsIterable[Repr], B)
- Implicit
- This member is added by an implicit conversion from IsIterable[Repr] toArrowAssoc[IsIterable[Repr]] performed by method ArrowAssoc in scala.Predef.
- Definition Classes
- ArrowAssoc
- Annotations
- @inline()
- final def ==(arg0: Any): Boolean
The expression
x == thatis equivalent toif (x eq null) that eq null else x.equals(that).The expression
x == thatis equivalent toif (x eq null) that eq null else x.equals(that).- returns
trueif the receiver object is equivalent to the argument;falseotherwise.
- Definition Classes
- AnyRef → Any
- final def asInstanceOf[T0]: T0
Cast the receiver object to be of type
T0.Cast the receiver object to be of type
T0.Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression
1.asInstanceOf[String]will throw aClassCastExceptionat runtime, while the expressionList(1).asInstanceOf[List[String]]will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.- returns
the receiver object.
- Definition Classes
- Any
- Exceptions thrown
ClassCastExceptionif the receiver object is not an instance of the erasure of typeT0.
- def clone(): AnyRef
Create a copy of the receiver object.
Create a copy of the receiver object.
The default implementation of the
clonemethod is platform dependent.- returns
a copy of the receiver object.
- def ensuring(cond: (IsIterable[Repr]) => Boolean, msg: => Any): IsIterable[Repr]
- Implicit
- This member is added by an implicit conversion from IsIterable[Repr] toEnsuring[IsIterable[Repr]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
- def ensuring(cond: (IsIterable[Repr]) => Boolean): IsIterable[Repr]
- Implicit
- This member is added by an implicit conversion from IsIterable[Repr] toEnsuring[IsIterable[Repr]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
- def ensuring(cond: Boolean, msg: => Any): IsIterable[Repr]
- Implicit
- This member is added by an implicit conversion from IsIterable[Repr] toEnsuring[IsIterable[Repr]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
- def ensuring(cond: Boolean): IsIterable[Repr]
- Implicit
- This member is added by an implicit conversion from IsIterable[Repr] toEnsuring[IsIterable[Repr]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
- final def eq(arg0: AnyRef): Boolean
Tests whether the argument (
that) is a reference to the receiver object (this).Tests whether the argument (
that) is a reference to the receiver object (this).The
eqmethod implements an equivalence relation on non-null instances ofAnyRef, and has three additional properties:- It is consistent: for any non-null instances
xandyof typeAnyRef, multiple invocations ofx.eq(y)consistently returnstrueor consistently returnsfalse. - For any non-null instance
xof typeAnyRef,x.eq(null)andnull.eq(x)returnsfalse. null.eq(null)returnstrue.
When overriding the
equalsorhashCodemethods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).- returns
trueif the argument is a reference to the receiver object;falseotherwise.
- Definition Classes
- AnyRef
- It is consistent: for any non-null instances
- def equals(arg0: AnyRef): Boolean
The equality method for reference types.
- def finalize(): Unit
Called by the garbage collector on the receiver object when there are no more references to the object.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the
finalizemethod is invoked, as well as the interaction betweenfinalizeand non-local returns and exceptions, are all platform dependent.- Attributes
- protected[lang]
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.Throwable])
- Note
not specified by SLS as a member of AnyRef
- final def getClass(): Class[_ <: AnyRef]
Returns the runtime class representation of the object.
- def hashCode(): Int
The hashCode method for reference types.
- final def isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object has the same erasure as
T0.Test whether the dynamic type of the receiver object has the same erasure as
T0.Depending on what
T0is, the test is done in one of the below ways:T0is a non-parameterized class type, e.g.BigDecimal: this method returnstrueif the value of the receiver object is aBigDecimalor a subtype ofBigDecimal.T0is a parameterized class type, e.g.List[Int]: this method returnstrueif the value of the receiver object is someList[X]for anyX. For example,List(1, 2, 3).isInstanceOf[List[String]]will return true.T0is some singleton typex.typeor literalx: this method returnsthis.eq(x). For example,x.isInstanceOf[1]is equivalent tox.eq(1)T0is an intersectionX with YorX & Y: this method is equivalent tox.isInstanceOf[X] && x.isInstanceOf[Y]T0is a unionX | Y: this method is equivalent tox.isInstanceOf[X] || x.isInstanceOf[Y]T0is a type parameter or an abstract type member: this method is equivalent toisInstanceOf[U]whereUisT0's upper bound,AnyifT0is unbounded. For example,x.isInstanceOf[A]whereAis an unbounded type parameter will return true for any value ofx.
This is exactly equivalent to the type pattern
_: T0- returns
trueif the receiver object is an instance of erasure of typeT0;falseotherwise.
- Definition Classes
- Any
- Note
due to the unexpectedness of
List(1, 2, 3).isInstanceOf[List[String]]returning true andx.isInstanceOf[A]whereAis a type parameter or abstract member returning true, these forms issue a warning.
- final def ne(arg0: AnyRef): Boolean
Equivalent to
!(this eq that).Equivalent to
!(this eq that).- returns
trueif the argument is not a reference to the receiver object;falseotherwise.
- Definition Classes
- AnyRef
- final def notify(): Unit
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up a single thread that is waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
- final def notifyAll(): Unit
Wakes up all threads that are waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
- final def synchronized[T0](arg0: => T0): T0
Executes the code in
bodywith an exclusive lock onthis.Executes the code in
bodywith an exclusive lock onthis.- returns
the result of
body
- Definition Classes
- AnyRef
- def toString(): String
Creates a String representation of this object.
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
- returns
a String representation of the object.
- Definition Classes
- AnyRef → Any
- final def wait(): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--.
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
- Note
not specified by SLS as a member of AnyRef
- final def wait(arg0: Long, arg1: Int): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
- Note
not specified by SLS as a member of AnyRef
- final def wait(arg0: Long): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.
Deprecated Value Members
- val conversion: (Repr) => IterableOps[A, Iterable, C]
- Definition Classes
- IsIterable → IsIterableOnce
- Annotations
- @deprecated
- Deprecated
(Since version 2.13.0) 'conversion' is now a method named 'apply'
- def formatted(fmtstr: String): String
Returns string formatted according to given
formatstring.Returns string formatted according to given
formatstring. Format strings are as forString.format(@see java.lang.String.format).- Implicit
- This member is added by an implicit conversion from IsIterable[Repr] toStringFormat[IsIterable[Repr]] performed by method StringFormat in scala.Predef.
- Definition Classes
- StringFormat
- Annotations
- @deprecated @inline()
- Deprecated
(Since version 2.12.16) Use
formatString.format(value)instead ofvalue.formatted(formatString), or use thef""string interpolator. In Java 15 and later,formattedresolves to the new method in String which has reversed parameters.
- def →[B](y: B): (IsIterable[Repr], B)
- Implicit
- This member is added by an implicit conversion from IsIterable[Repr] toArrowAssoc[IsIterable[Repr]] performed by method ArrowAssoc in scala.Predef.
- Definition Classes
- ArrowAssoc
- Annotations
- @deprecated
- Deprecated
(Since version 2.13.0) Use
->instead. If you still wish to display it as one character, consider using a font with programming ligatures such as Fira Code.
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int,Float,ArrayorOptionwhich are accessible in all Scala compilation units without explicit qualification or imports.Notable packages include:
scala.collectionand its sub-packages contain Scala's collections frameworkscala.collection.immutable- Immutable, sequential data-structures such asVector,List,Range,HashMaporHashSetscala.collection.mutable- Mutable, sequential data-structures such asArrayBuffer,StringBuilder,HashMaporHashSetscala.collection.concurrent- Mutable, concurrent data-structures such asTrieMapscala.concurrent- Primitives for concurrent programming such asFuturesandPromisesscala.io- Input and output operationsscala.math- Basic math functions and additional numeric types likeBigIntandBigDecimalscala.sys- Interaction with other processes and the operating systemscala.util.matching- Regular expressionsOther packages exist. See the complete list on the right.
Additional parts of the standard library are shipped as separate libraries. These include:
scala.reflect- Scala's reflection API (scala-reflect.jar)scala.xml- XML parsing, manipulation, and serialization (scala-xml.jar)scala.collection.parallel- Parallel collections (scala-parallel-collections.jar)scala.util.parsing- Parser combinators (scala-parser-combinators.jar)scala.swing- A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)Automatic imports
Identifiers in the scala package and the
scala.Predefobject are always in scope by default.Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example,
Listis an alias forscala.collection.immutable.List.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
Stringis an alias forjava.lang.String.