object Exception
Classes representing the components of exception handling.
Each class is independently composable.
This class differs from scala.util.Try in that it focuses on composing exception handlers rather than
composing behavior. All behavior should be composed first and fed to a Catch object using one of the
opt, either or withTry methods. Taken together the classes provide a DSL for composing catch and finally
behaviors.
Examples
Create a Catch which handles specified exceptions.
import scala.util.control.Exception._ import java.net._ val s = "http://www.scala-lang.org/" // Some(http://www.scala-lang.org/) val x1: Option[URL] = catching(classOf[MalformedURLException]) opt new URL(s) // Right(http://www.scala-lang.org/) val x2: Either[Throwable,URL] = catching(classOf[MalformedURLException], classOf[NullPointerException]) either new URL(s) // Success(http://www.scala-lang.org/) val x3: Try[URL] = catching(classOf[MalformedURLException], classOf[NullPointerException]) withTry new URL(s) val defaultUrl = new URL("http://example.com") // URL(http://example.com) because htt/xx throws MalformedURLException val x4: URL = failAsValue(classOf[MalformedURLException])(defaultUrl)(new URL("htt/xx"))
Create a Catch which logs exceptions using handling and by.
def log(t: Throwable): Unit = t.printStackTrace val withThrowableLogging: Catch[Unit] = handling(classOf[MalformedURLException]) by (log) def printUrl(url: String) : Unit = { val con = new URL(url) openConnection() val source = scala.io.Source.fromInputStream(con.getInputStream()) source.getLines.foreach(println) } val badUrl = "htt/xx" // Prints stacktrace, // java.net.MalformedURLException: no protocol: htt/xx // at java.net.URL.(URL.java:586) withThrowableLogging { printUrl(badUrl) } val goodUrl = "http://www.scala-lang.org/" // Prints page content, // <!DOCTYPE html> // <html> withThrowableLogging { printUrl(goodUrl) }
Use unwrapping to create a Catch that unwraps exceptions before rethrowing.
class AppException(cause: Throwable) extends RuntimeException(cause) val unwrappingCatch: Catch[Nothing] = unwrapping(classOf[AppException]) def calcResult: Int = throw new AppException(new NullPointerException) // Throws NPE not AppException, // java.lang.NullPointerException // at .calcResult(<console>:17) val result = unwrappingCatch(calcResult)
Use failAsValue to provide a default when a specified exception is caught.
val inputDefaulting: Catch[Int] = failAsValue(classOf[NumberFormatException])(0) val candidatePick = "seven" // scala.io.StdIn.readLine() // Int = 0 val pick = inputDefaulting(candidatePick.toInt)
Compose multiple Catchs with or to build a Catch that provides default values varied by exception.
val formatDefaulting: Catch[Int] = failAsValue(classOf[NumberFormatException])(0) val nullDefaulting: Catch[Int] = failAsValue(classOf[NullPointerException])(-1) val otherDefaulting: Catch[Int] = nonFatalCatch withApply(_ => -100) val combinedDefaulting: Catch[Int] = formatDefaulting or nullDefaulting or otherDefaulting def p(s: String): Int = s.length * s.toInt // Int = 0 combinedDefaulting(p("tenty-nine")) // Int = -1 combinedDefaulting(p(null: String)) // Int = -100 combinedDefaulting(throw new IllegalStateException) // Int = 22 combinedDefaulting(p("11"))
- Source
- Exception.scala
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Type Members
- class By[T, R] extends AnyRef
-
class
Catch[+T] extends Described
A container class for catch/finally logic.
A container class for catch/finally logic.
Pass a different value for rethrow if you want to probably unwisely allow catching control exceptions and other throwables which the rest of the world may expect to get through.
- T
result type of bodies used in try and catch blocks
- type Catcher[+T] = PartialFunction[Throwable, T]
- trait Described extends AnyRef
-
class
Finally extends Described
A container class for finally code.
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
-
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
allCatch[T]: Catch[T]
A
Catchobject which catches everything. - final def allCatcher[T]: Catcher[T]
-
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 catching[T](c: Catcher[T]): Catch[T]
-
def
catching[T](exceptions: Class[_]*): Catch[T]
Creates a
Catchobject which will catch any of the supplied exceptions.Creates a
Catchobject which will catch any of the supplied exceptions. Since the returnedCatchobject has no specific logic defined and will simply rethrow the exceptions it catches, you will typically want to callopt,eitherorwithTryon the return value, or assign custom logic by calling "withApply".Note that
Catchobjects automatically rethrowControlExceptionsand others which should only be caught in exceptional circumstances. If you really want to catch exactly what you specify, usecatchingPromiscuouslyinstead. - def catchingPromiscuously[T](c: Catcher[T]): Catch[T]
-
def
catchingPromiscuously[T](exceptions: Class[_]*): Catch[T]
Creates a
Catchobject which will catch any of the supplied exceptions.Creates a
Catchobject which will catch any of the supplied exceptions. Unlike "catching" which filters out those in shouldRethrow, this one will catch whatever you ask of it includingControlThrowableorInterruptedException. -
def
clone(): AnyRef
Create a copy of the receiver object.
-
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: Any): Boolean
The equality method for reference types.
-
def
failAsValue[T](exceptions: Class[_]*)(value: ⇒ T): Catch[T]
Creates a
Catchobject which maps all the supplied exceptions to the given value. -
def
failing[T](exceptions: Class[_]*): Catch[Option[T]]
Creates a
Catchobject which maps all the supplied exceptions toNone. -
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. -
final
def
getClass(): Class[_]
Returns the runtime class representation of the object.
-
def
handling[T](exceptions: Class[_]*): By[(Throwable) ⇒ T, Catch[T]]
Returns a partially constructed
Catchobject, which you must give an exception handler function as an argument toby.Returns a partially constructed
Catchobject, which you must give an exception handler function as an argument toby.handling(classOf[MalformedURLException], classOf[NullPointerException]) by (_.printStackTrace)
Example: -
def
hashCode(): Int
The hashCode method for reference types.
-
def
ignoring(exceptions: Class[_]*): Catch[Unit]
Creates a
Catchobject which catches and ignores any of the supplied exceptions. -
final
def
isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object is
T0.Test whether the dynamic type of the receiver object is
T0.Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression
1.isInstanceOf[String]will returnfalse, while the expressionList(1).isInstanceOf[List[String]]will returntrue. 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 specified type.- returns
trueif the receiver object is an instance of erasure of typeT0;falseotherwise.
- Definition Classes
- Any
- def mkCatcher[Ex <: Throwable, T](isDef: (Ex) ⇒ Boolean, f: (Ex) ⇒ T)(implicit arg0: ClassTag[Ex]): Catcher[T]
- def mkThrowableCatcher[T](isDef: (Throwable) ⇒ Boolean, f: (Throwable) ⇒ T): Catcher[T]
-
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
val
noCatch: Catch[Nothing]
The empty
Catchobject. -
final
def
nonFatalCatch[T]: Catch[T]
A
Catchobject which catches non-fatal exceptions. - final def nonFatalCatcher[T]: Catcher[T]
- final val nothingCatcher: Catcher[Nothing]
-
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
-
def
shouldRethrow(x: Throwable): Boolean
!!! Not at all sure of every factor which goes into this, and/or whether we need multiple standard variations.
!!! Not at all sure of every factor which goes into this, and/or whether we need multiple standard variations.
- returns
true if
xisControlThrowableorInterruptedExceptionotherwise false.
-
final
def
synchronized[T0](arg0: ⇒ T0): T0
- Definition Classes
- AnyRef
- implicit def throwableSubtypeToCatcher[Ex <: Throwable, T](pf: PartialFunction[Ex, T])(implicit arg0: ClassTag[Ex]): Catcher[T]
-
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
-
def
ultimately[T](body: ⇒ Unit): Catch[T]
Returns a
Catchobject with no catch logic and the argument as the finally logic. -
def
unwrapping[T](exceptions: Class[_]*): Catch[T]
Creates a
Catchobject which unwraps any of the supplied exceptions. -
final
def
wait(): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
-
final
def
wait(arg0: Long, arg1: Int): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
- final def wait(arg0: Long): Unit
Catch behavior composition
Build Catch objects from exception lists and catch logic
Finally behavior composition
Build Catch objects from finally logic
General purpose catch objects
Catch objects with predefined behavior. Use combinator methods to compose additional behavior.
DSL behavior composition
Expressive Catch behavior composition
Promiscuous Catch behaviors
Useful if catching ControlThrowable or InterruptedException is required.
Logic Containers
Containers for catch and finally behavior.
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.collection.parallel.immutable- Immutable, parallel data-structures such asParVector,ParRange,ParHashMaporParHashSetscala.collection.parallel.mutable- Mutable, parallel data-structures such asParArray,ParHashMap,ParTrieMaporParHashSetscala.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.swing- A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)scala.util.parsing- Parser combinators (scala-parser-combinators.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.