scala API Predef

╰半橙微兮° 2023-07-13 12:23 54阅读 0赞

Predef 对象提供了可以在所有 Scala 编译单元中访问的定义，而不需要显式限定。

# 常用的类型 #

Predef为常用的类型提供类型别名，例如不可变集合类型 [scala.collection.immutable.Map][], [scala.collection.immutable.Set][], and the [scala.collection.immutable.List][] constructors ([scala.collection.immutable.::][scala.collection.immutable.] and [scala.collection.immutable.Nil][]).

# Console I/O #

Predef 为控制台 I/O 提供了许多简单的函数，如 print、println、readLine、readInt 等。这些函数都是 scala.Console 提供的函数的别名。

# 断言 #

提供了一组 assert 函数，用于记录和动态检查代码中的不变量。通过提供命令行选项 `-Xdisable-assertions`，可以在编译时省略对断言的调用，该选项在 `elidable.ASSERTION `引出- xlib。指向scalac命令。

还提供了用于静态分析工具的各种断言:`assume`, `require` and `ensuring`. `require` 和 `ensuring `用于作为函数的前置和后置条件的契约式设计样式规范的一种手段，目的是使这些规范能够被静态分析工具使用。例如,

>     def addNaturals(nats: List[Int]): Int = {
>       require(nats forall (_ >= 0), "List contains negative numbers")
>       nats.foldLeft(0)(_ + _)
>     } ensuring(_ >= 0)

addNaturals 声明传递的整数列表应该只包含自然数(即非负数)，并且返回的结果也应该是自然数。**require 与 assert 的不同之处在于，如果条件失败，那么应该归咎于函数的调用者，而不是在 addNaturals 本身中发生的逻辑错误。**ensure 是一种断言形式，它声明了函数所提供的关于其返回值的保证。

# 隐式转换 #

这里还定义了一些常用的隐式转换，以及父类型 scala.LowPriorityImplicits。为数值的“扩展”提供了隐式转换，例如，根据需要将短值转换为长值，并向数组值添加额外的高阶函数。这些在 [scala.Array][] 的文档中有更详细的描述。

# Type Members #

*  sealed abstract class [<:<][Link 1]\[-From, +To\] extends (From) ⇒ To with [Serializable][]
    
    An instance of `A <:< B` witnesses that `A` is a subtype of `B`.
 *   
    
    sealed abstract class [=:=][Link 2]\[From, To\] extends (From) ⇒ To with [Serializable][]
    
    An instance of `A =:= B` witnesses that the types `A` and `B` are equal.
 *   
    
    implicit final class [ArrayCharSequence][] extends CharSequence
 *   
    
    implicit final class [ArrowAssoc][]\[A\] extends [AnyVal][]
 *   
    
    type Class\[T\] = java.lang.Class\[T\]
 *   
    
    class [DummyImplicit][] extends [AnyRef][]
    
    总是有一个隐式值的类型。
 *   
    
    implicit final class [Ensuring][]\[A\] extends [AnyVal][]
 *   
    
    type Function\[-A, +B\] = (A) ⇒ B
 *   
    
    type Manifest\[T\] = [reflect.Manifest][]\[T\]
 *   
    
    type Map\[A, +B\] = [collection.immutable.Map][scala.collection.immutable.Map]\[A, B\]
 *   
    
    type OptManifest\[T\] = [reflect.OptManifest][]\[T\]
 *   
    
    implicit final class [RichException][] extends [AnyVal][]
 *   
    
    implicit final class [SeqCharSequence][] extends CharSequence
 *   
    
    type Set\[A\] = [collection.immutable.Set][scala.collection.immutable.Set]\[A\]
 *   
    
    type String = java.lang.String
    
    Scala 中的字符串类型有来自底层Java字符串的方法，也有通过scala.collection.immutable.StringOps隐式添加的方法。
 *   
    
    implicit final class [StringFormat][]\[A\] extends [AnyVal][]
 *   
    
    implicit final class [any2stringadd][]\[A\] extends [AnyVal][]
 *   
    
    type ClassManifest\[T\] = [ClassTag][]\[T\]
    
    [ ][Link 3]
 *   
    
    type Pair\[+A, +B\] = (A, B)
 *   
    
    type Triple\[+A, +B, +C\] = (A, B, C)

# Value Members #

*  implicit def $conforms\[A\]: [<:<][Link 1]\[A, A\]
 *   
    
    object [=:=][Link 4] extends [Serializable][]
 *  def ???: [Nothing][]
    
    `???` 可用于标记仍有待实现的方法。
 *   
    
    implicit def **Boolean2boolean**(x: java.lang.Boolean): [Boolean][]
 *   
    
    implicit def **Byte2byte**(x: java.lang.Byte): [Byte][]
 *   
    
    implicit def **Character2char**(x: Character): [Char][]
 *   
    
    implicit def **Double2double**(x: java.lang.Double): [Double][]
 *  object **[DummyImplicit][DummyImplicit 1]**
 *   
    
    implicit def **Float2float**(x: java.lang.Float): [Float][]
 *   
    
    implicit def **Integer2int**(x: Integer): [Int][]
 *   
    
    implicit def **Long2long**(x: java.lang.Long): [Long][]
 *   
    
    val Manifest: [ManifestFactory][].type
 *   
    
    val Map: [collection.immutable.Map][].type
 *  val NoManifest: [reflect.NoManifest][].type
 *   
    
    val Set: [collection.immutable.Set][].type
 *   
    
    implicit def **Short2short**(x: java.lang.Short): [Short][]
 *   
    
    implicit val StringCanBuildFrom: [CanBuildFrom][]\[[String][], [Char][], [String][]\]
 *   
    
    final def **assert**(assertion: [Boolean][], message: ⇒ [Any][]): [Unit][]
    
    测试表达式，如果为假则抛出AssertionError。
 *   
    
    def **assert**(assertion: [Boolean][]): [Unit][]
    
    测试表达式，如果为假则抛出AssertionError。
 *   
    
    final def **assume**(assumption: [Boolean][], message: ⇒ [Any][]): [Unit][]
    
    测试表达式，如果为假则抛出AssertionError。
 *   
    
    def **assume**(assumption: [Boolean][]): [Unit][]
    
    测试表达式，如果为假则抛出AssertionError。
 *   
    
    implicit def **augmentString**(x: [String][]): [StringOps][]
 *   
    
    implicit def **boolean2Boolean**(x: [Boolean][]): java.lang.Boolean
 *   
    
    implicit def **booleanArrayOps**(xs: [Array][scala.Array]\[[Boolean][]\]): [ArrayOps][]\[[Boolean][]\]
 *   
    
    implicit def **booleanWrapper**(x: [Boolean][]): [RichBoolean][]
 *   
    
    implicit def **byte2Byte**(x: [Byte][]): java.lang.Byte
 *   
    
    implicit def **byteArrayOps**(xs: [Array][scala.Array]\[[Byte][]\]): [ArrayOps][]\[[Byte][]\]
 *   
    
    implicit def **byteWrapper**(x: [Byte][]): [RichByte][]
    
    我们更喜欢java.lang。\*在任何潜在的冲突中，将类型装入这些包装器。
 *   
    
    implicit def **char2Character**(x: [Char][]): Character
 *   
    
    implicit def **charArrayOps**(xs: [Array][scala.Array]\[[Char][]\]): [ArrayOps][]\[[Char][]\]
 *   
    
    implicit def **charWrapper**(c: [Char][]): [RichChar][]
 *  def **classOf**\[T\]: [Class][]\[T\]
    
    检索类类型的运行时表示形式。
 *   
    
    implicit def **double2Double**(x: [Double][]): java.lang.Double
 *   
    
    implicit def **doubleArrayOps**(xs: [Array][scala.Array]\[[Double][]\]): [ArrayOps][]\[[Double][]\]
 *   
    
    implicit def **doubleWrapper**(x: [Double][]): [RichDouble][]
 *   
    
    implicit def **fallbackStringCanBuildFrom**\[T\]: [CanBuildFrom][]\[[String][], T, [collection.immutable.IndexedSeq][]\[T\]\]
 *   
    
    implicit def **float2Float**(x: [Float][]): java.lang.Float
 *   
    
    implicit def **floatArrayOps**(xs: [Array][scala.Array]\[[Float][]\]): [ArrayOps][]\[[Float][]\]
 *   
    
    implicit def **floatWrapper**(x: [Float][]): [RichFloat][]
 *   
    
    implicit def **genericArrayOps**\[T\](xs: [Array][scala.Array]\[T\]): [ArrayOps][]\[T\]
 *   
    
    implicit def **genericWrapArray**\[T\](xs: [Array][scala.Array]\[T\]): [WrappedArray][]\[T\]
 *   
    
    def **identity**\[A\](x: A): A
 *   
    
    def **implicitly**\[T\](implicit e: T): T
 *   
    
    implicit def **int2Integer**(x: [Int][]): Integer
 *   
    
    implicit def **intArrayOps**(xs: [Array][scala.Array]\[[Int][]\]): [ArrayOps][]\[[Int][]\]
 *   
    
    implicit def **intWrapper**(x: [Int][]): [RichInt][]
 *   
    
    def **locally**\[T\](x: T): T
 *   
    
    implicit def **long2Long**(x: [Long][]): java.lang.Long
 *   
    
    implicit def **longArrayOps**(xs: [Array][scala.Array]\[[Long][]\]): [ArrayOps][]\[[Long][]\]
 *   
    
    implicit def **longWrapper**(x: [Long][]): [RichLong][]
 *   
    
    def **manifest**\[T\](implicit m: [Manifest][]\[T\]): [Manifest][]\[T\]
 *   
    
    def **optManifest**\[T\](implicit m: [OptManifest][]\[T\]): [OptManifest][]\[T\]
 *   
    
    def **print**(x: [Any][]): [Unit][]
 *   
    
    def **printf**(text: [String][], xs: [Any][]\*): [Unit][]
 *   
    
    def **println**(x: [Any][]): [Unit][]
 *  def **println**(): [Unit][]
 *   
    
    implicit def **refArrayOps**\[T <: [AnyRef][]\](xs: [Array][scala.Array]\[T\]): [ArrayOps][]\[T\]
 *   
    
    final def **require**(requirement: [Boolean][], message: ⇒ [Any][]): [Unit][]
    
    测试一个表达式，如果为假则抛出一个IllegalArgumentException。
 *   
    
    def **require**(requirement: [Boolean][]): [Unit][]
    
    测试一个表达式，如果为假则抛出一个IllegalArgumentException。
 *   
    
    implicit def **short2Short**(x: [Short][]): java.lang.Short
 *   
    
    implicit def **shortArrayOps**(xs: [Array][scala.Array]\[[Short][]\]): [ArrayOps][]\[[Short][]\]
 *   
    
    implicit def **shortWrapper**(x: [Short][]): [RichShort][]
 *   
    
    implicit def **tuple2ToZippedOps**\[T1, T2\](x: (T1, T2)): [Ops][]\[T1, T2\]
 *   
    
    implicit def **tuple3ToZippedOps**\[T1, T2, T3\](x: (T1, T2, T3)): [Ops][Ops 1]\[T1, T2, T3\]
 *   
    
    implicit def **unaugmentString**(x: [StringOps][]): [String][]
 *   
    
    implicit def **unitArrayOps**(xs: [Array][scala.Array]\[[Unit][]\]): [ArrayOps][]\[[Unit][]\]
 *   
    
    implicit def **unwrapString**(ws: [WrappedString][]): [String][]
 *   
    
    implicit def **wrapBooleanArray**(xs: [Array][scala.Array]\[[Boolean][]\]): [WrappedArray][]\[[Boolean][]\]
 *   
    
    implicit def **wrapByteArray**(xs: [Array][scala.Array]\[[Byte][]\]): [WrappedArray][]\[[Byte][]\]
 *   
    
    implicit def **wrapCharArray**(xs: [Array][scala.Array]\[[Char][]\]): [WrappedArray][]\[[Char][]\]
 *   
    
    implicit def **wrapDoubleArray**(xs: [Array][scala.Array]\[[Double][]\]): [WrappedArray][]\[[Double][]\]
 *   
    
    implicit def **wrapFloatArray**(xs: [Array][scala.Array]\[[Float][]\]): [WrappedArray][]\[[Float][]\]
 *   
    
    implicit def **wrapIntArray**(xs: [Array][scala.Array]\[[Int][]\]): [WrappedArray][]\[[Int][]\]
 *   
    
    implicit def **wrapLongArray**(xs: [Array][scala.Array]\[[Long][]\]): [WrappedArray][]\[[Long][]\]
 *   
    
    implicit def **wrapRefArray**\[T <: [AnyRef][]\](xs: [Array][scala.Array]\[T\]): [WrappedArray][]\[T\]
 *   
    
    implicit def **wrapShortArray**(xs: [Array][scala.Array]\[[Short][]\]): [WrappedArray][]\[[Short][]\]
 *   
    
    implicit def **wrapString**(s: [String][]): [WrappedString][]
 *   
    
    implicit def **wrapUnitArray**(xs: [Array][scala.Array]\[[Unit][]\]): [WrappedArray][]\[[Unit][]\]

# Deprecated Value Members #

*  val ClassManifest: [ClassManifestFactory][].type
 *   
    
    object [Pair][]
 *   
    
    object [Triple][]
 *   
    
    def any2ArrowAssoc\[A\](x: A): [ArrowAssoc][]\[A\]
 *   
    
    def any2Ensuring\[A\](x: A): [Ensuring][]\[A\]
 *   
    
    def any2stringfmt(x: [Any][]): [StringFormat][]\[[Any][]\]
 *   
    
    def arrayToCharSequence(xs: [Array][scala.Array]\[[Char][]\]): CharSequence
 *   
    
    def classManifest\[T\](implicit m: [ClassManifest][]\[T\]): [ClassManifest][]\[T\]
 *  def conforms\[A\]: [<:<][Link 1]\[A, A\]
 *   
    
    def error(message: [String][]): [Nothing][]
 *   
    
    def exceptionWrapper(exc: scala.Throwable): [RichException][]
 *  def readBoolean(): [Boolean][]
 *  def readByte(): [Byte][]
 *  def readChar(): [Char][]
 *  def readDouble(): [Double][]
 *  def readFloat(): [Float][]
 *  def readInt(): [Int][]
 *   
    
    def readLine(text: [String][], args: [Any][]\*): [String][]
 *   
    
    def readLine(): [String][]
    
    [ ][Link 5]
 *  def readLong(): [Long][]
 *  def readShort(): [Short][]
 *   
    
    def readf(format: [String][]): [List][]\[[Any][]\]
 *   
    
    def readf1(format: [String][]): [Any][]
 *   
    
    def readf2(format: [String][]): ([Any][], [Any][])
 *   
    
    def readf3(format: [String][]): ([Any][], [Any][], [Any][])
 *   
    
    def seqToCharSequence(xs: [collection.IndexedSeq][]\[[Char][]\]): CharSequence

原文地址：[https://www.scala-lang.org/api/2.11.12/\#scala.Predef$][https_www.scala-lang.org_api_2.11.12_scala.Predef]

[scala.collection.immutable.Map]: https://www.scala-lang.org/api/2.11.12/scala/collection/immutable/Map.html
[scala.collection.immutable.Set]: https://www.scala-lang.org/api/2.11.12/scala/collection/immutable/Set.html
[scala.collection.immutable.List]: https://www.scala-lang.org/api/2.11.12/scala/collection/immutable/List.html
[scala.collection.immutable.]: https://www.scala-lang.org/api/2.11.12/scala/collection/immutable/$colon$colon.html
[scala.collection.immutable.Nil]: https://www.scala-lang.org/api/2.11.12/scala/collection/immutable/Nil$.html
[scala.Array]: https://www.scala-lang.org/api/2.11.12/scala/Array.html
[Link 1]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$$less$colon$less.html
[Serializable]: https://www.scala-lang.org/api/2.11.12/scala/Serializable.html
[Link 2]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$$eq$colon$eq.html
[ArrayCharSequence]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$ArrayCharSequence.html
[ArrowAssoc]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$ArrowAssoc.html
[AnyVal]: https://www.scala-lang.org/api/2.11.12/scala/AnyVal.html
[DummyImplicit]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$DummyImplicit.html
[AnyRef]: https://www.scala-lang.org/api/2.11.12/scala/AnyRef.html
[Ensuring]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$Ensuring.html
[reflect.Manifest]: https://www.scala-lang.org/api/2.11.12/scala/reflect/Manifest.html
[reflect.OptManifest]: https://www.scala-lang.org/api/2.11.12/scala/reflect/OptManifest.html
[RichException]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$RichException.html
[SeqCharSequence]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$SeqCharSequence.html
[StringFormat]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$StringFormat.html
[any2stringadd]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$any2stringadd.html
[ClassTag]: https://www.scala-lang.org/api/2.11.12/scala/reflect/ClassTag.html
[Link 3]: https://www.scala-lang.org/api/2.11.12/index.html#scala.Predef$@ClassManifest%5BT%5D=reflect.ClassManifest%5BT%5D
[Link 4]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$$eq$colon$eq$.html
[Nothing]: https://www.scala-lang.org/api/2.11.12/scala/Nothing.html
[Boolean]: https://www.scala-lang.org/api/2.11.12/scala/Boolean.html
[Byte]: https://www.scala-lang.org/api/2.11.12/scala/Byte.html
[Char]: https://www.scala-lang.org/api/2.11.12/scala/Char.html
[Double]: https://www.scala-lang.org/api/2.11.12/scala/Double.html
[DummyImplicit 1]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$DummyImplicit$.html
[Float]: https://www.scala-lang.org/api/2.11.12/scala/Float.html
[Int]: https://www.scala-lang.org/api/2.11.12/scala/Int.html
[Long]: https://www.scala-lang.org/api/2.11.12/scala/Long.html
[ManifestFactory]: https://www.scala-lang.org/api/2.11.12/scala/reflect/ManifestFactory$.html
[collection.immutable.Map]: https://www.scala-lang.org/api/2.11.12/scala/collection/immutable/Map$.html
[reflect.NoManifest]: https://www.scala-lang.org/api/2.11.12/scala/reflect/NoManifest$.html
[collection.immutable.Set]: https://www.scala-lang.org/api/2.11.12/scala/collection/immutable/Set$.html
[Short]: https://www.scala-lang.org/api/2.11.12/scala/Short.html
[CanBuildFrom]: https://www.scala-lang.org/api/2.11.12/scala/collection/generic/CanBuildFrom.html
[String]: https://www.scala-lang.org/api/2.11.12/scala/Predef$.html#String=String
[Any]: https://www.scala-lang.org/api/2.11.12/scala/Any.html
[Unit]: https://www.scala-lang.org/api/2.11.12/scala/Unit.html
[StringOps]: https://www.scala-lang.org/api/2.11.12/scala/collection/immutable/StringOps.html
[ArrayOps]: https://www.scala-lang.org/api/2.11.12/scala/collection/mutable/ArrayOps.html
[RichBoolean]: https://www.scala-lang.org/api/2.11.12/scala/runtime/RichBoolean.html
[RichByte]: https://www.scala-lang.org/api/2.11.12/scala/runtime/RichByte.html
[RichChar]: https://www.scala-lang.org/api/2.11.12/scala/runtime/RichChar.html
[Class]: https://www.scala-lang.org/api/2.11.12/scala/Predef$.html#Class%5BT%5D=Class%5BT%5D
[RichDouble]: https://www.scala-lang.org/api/2.11.12/scala/runtime/RichDouble.html
[collection.immutable.IndexedSeq]: https://www.scala-lang.org/api/2.11.12/scala/collection/immutable/IndexedSeq.html
[RichFloat]: https://www.scala-lang.org/api/2.11.12/scala/runtime/RichFloat.html
[WrappedArray]: https://www.scala-lang.org/api/2.11.12/scala/collection/mutable/WrappedArray.html
[RichInt]: https://www.scala-lang.org/api/2.11.12/scala/runtime/RichInt.html
[RichLong]: https://www.scala-lang.org/api/2.11.12/scala/runtime/RichLong.html
[Manifest]: https://www.scala-lang.org/api/2.11.12/scala/Predef$.html#Manifest%5BT%5D=scala.reflect.Manifest%5BT%5D
[OptManifest]: https://www.scala-lang.org/api/2.11.12/scala/Predef$.html#OptManifest%5BT%5D=scala.reflect.OptManifest%5BT%5D
[RichShort]: https://www.scala-lang.org/api/2.11.12/scala/runtime/RichShort.html
[Ops]: https://www.scala-lang.org/api/2.11.12/scala/runtime/Tuple2Zipped$$Ops.html
[Ops 1]: https://www.scala-lang.org/api/2.11.12/scala/runtime/Tuple3Zipped$$Ops.html
[WrappedString]: https://www.scala-lang.org/api/2.11.12/scala/collection/immutable/WrappedString.html
[ClassManifestFactory]: https://www.scala-lang.org/api/2.11.12/scala/reflect/ClassManifestFactory$.html
[Pair]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$Pair$.html
[Triple]: https://www.scala-lang.org/api/2.11.12/scala/Predef$$Triple$.html
[ClassManifest]: https://www.scala-lang.org/api/2.11.12/scala/Predef$.html#ClassManifest%5BT%5D=reflect.ClassManifest%5BT%5D
[Link 5]: https://www.scala-lang.org/api/2.11.12/index.html#scala.Predef$@readLine%28%29:DeprecatedPredef.this.String
[List]: https://www.scala-lang.org/api/2.11.12/scala/package.html#List%5B+A%5D=List%5BA%5D
[collection.IndexedSeq]: https://www.scala-lang.org/api/2.11.12/scala/collection/IndexedSeq.html
[https_www.scala-lang.org_api_2.11.12_scala.Predef]: https://www.scala-lang.org/api/2.11.12/#scala.Predef$