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 String
s (String
s
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
- Show All
- 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
Repr
itself, 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
Repr
toIterableOps[A, Iterable, C]
A conversion from the type
Repr
toIterableOps[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
true
if !(this == that), false otherwise.
- Definition Classes
- AnyRef → Any
- final def ##: Int
Equivalent to
x.hashCode
except for boxed numeric types andnull
.Equivalent to
x.hashCode
except 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. Fornull
returns a hashcode wherenull.hashCode
throws 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 == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.- returns
true
if the receiver object is equivalent to the argument;false
otherwise.
- Definition Classes
- AnyRef → Any
- final def asInstanceOf[T0]: T0
Forces the compiler to treat the receiver object as having type
T0
, even though doing so may violate type safety.Forces the compiler to treat the receiver object as having type
T0
, even though doing so may violate type safety.This method is useful when you believe you have type information the compiler doesn't, and it also isn't possible to check the type at runtime. In such situations, skipping type safety is the only option.
It is platform dependent whether
asInstanceOf
has any effect at runtime. It might do a runtime type test on the erasure ofT0
, insert a conversion (such as boxing/unboxing), fill in a default value, or do nothing at all.In particular,
asInstanceOf
is not a type test. It does **not** mean:this match { case x: T0 => x case _ => throw ClassCastException("...")
Use pattern matching or isInstanceOf for type testing instead.
Situations where
asInstanceOf
is useful:- when flow analysis fails to deduce
T0
automatically - when down-casting a type parameter or an abstract type member (which cannot be checked at runtime due to type erasure) If there is any doubt and you are able to type test instead, you should do so.
Be careful of using
asInstanceOf
whenT0
is a primitive type. WhenT0
is primitive,asInstanceOf
may insert a conversion instead of a type test. If your intent is to convert, use atoT
method (x.toChar
,x.toByte
, etc.).- returns
the receiver object.
- Definition Classes
- Any
- Exceptions thrown
ClassCastException
if the receiver is not an instance of the erasure ofT0
, if that can be checked on this platform
- when flow analysis fails to deduce
- def clone(): AnyRef
Create a copy of the receiver object.
Create a copy of the receiver object.
The default implementation of the
clone
method 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
eq
method implements an equivalence relation on non-null instances ofAnyRef
, and has three additional properties:- It is consistent: for any non-null instances
x
andy
of typeAnyRef
, multiple invocations ofx.eq(y)
consistently returnstrue
or consistently returnsfalse
. - For any non-null instance
x
of typeAnyRef
,x.eq(null)
andnull.eq(x)
returnsfalse
. null.eq(null)
returnstrue
.
When overriding the
equals
orhashCode
methods, 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
true
if the argument is a reference to the receiver object;false
otherwise.
- 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
finalize
method is invoked, as well as the interaction betweenfinalize
and 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
T0
is, the test is done in one of the below ways:T0
is a non-parameterized class type, e.g.BigDecimal
: this method returnstrue
if the value of the receiver object is aBigDecimal
or a subtype ofBigDecimal
.T0
is a parameterized class type, e.g.List[Int]
: this method returnstrue
if the value of the receiver object is someList[X]
for anyX
. For example,List(1, 2, 3).isInstanceOf[List[String]]
will return true.T0
is some singleton typex.type
or literalx
: this method returnsthis.eq(x)
. For example,x.isInstanceOf[1]
is equivalent tox.eq(1)
T0
is an intersectionX with Y
orX & Y: this method is equivalent to
x.isInstanceOf[X] && x.isInstanceOf[Y]T0
is a unionX | Y
: this method is equivalent tox.isInstanceOf[X] || x.isInstanceOf[Y]
T0
is a type parameter or an abstract type member: this method is equivalent toisInstanceOf[U]
whereU
isT0
's upper bound,Any
ifT0
is unbounded. For example,x.isInstanceOf[A]
whereA
is an unbounded type parameter will return true for any value ofx
.
This is exactly equivalent to the type pattern
_: T0
- returns
true
if the receiver object is an instance of erasure of typeT0
;false
otherwise.
- Definition Classes
- Any
- Note
due to the unexpectedness of
List(1, 2, 3).isInstanceOf[List[String]]
returning true andx.isInstanceOf[A]
whereA
is 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
true
if the argument is not a reference to the receiver object;false
otherwise.
- 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
body
with an exclusive lock onthis
.Executes the code in
body
with 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
format
string.Returns string formatted according to given
format
string. 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,formatted
resolves 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
,Array
orOption
which are accessible in all Scala compilation units without explicit qualification or imports.Notable packages include:
scala.collection
and its sub-packages contain Scala's collections frameworkscala.collection.immutable
- Immutable, sequential data-structures such asVector
,List
,Range
,HashMap
orHashSet
scala.collection.mutable
- Mutable, sequential data-structures such asArrayBuffer
,StringBuilder
,HashMap
orHashSet
scala.collection.concurrent
- Mutable, concurrent data-structures such asTrieMap
scala.concurrent
- Primitives for concurrent programming such asFutures
andPromises
scala.io
- Input and output operationsscala.math
- Basic math functions and additional numeric types likeBigInt
andBigDecimal
scala.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.Predef
object are always in scope by default.Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example,
List
is an alias forscala.collection.immutable.List
.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
String
is an alias forjava.lang.String
.