Try

scala.util.Try

See theTry companion object

sealed abstract class Try[+T] extends Product, Serializable

The Try type represents a computation that may fail during evaluation by raising an exception. It holds either a successfully computed value or the exception that was thrown. This is similar to the scala.util.Either type, but with different semantics.

Instances of Try[T] are an instance of either scala.util.Success[T] or scala.util.Failure[T].

For example, consider a computation that performs division on user-defined input. Try can reduce or eliminate the need for explicit exception handling in all of the places where an exception might be thrown.

Example:

import scala.io.StdIn
import scala.util.{Try, Success, Failure}

def divide: Try[Int] = {
  val dividend = Try(StdIn.readLine("Enter an Int that you'd like to divide:\n").toInt)
  val divisor = Try(StdIn.readLine("Enter an Int that you'd like to divide by:\n").toInt)
  val problem = dividend.flatMap(x => divisor.map(y => x/y))
  problem match {
    case Success(v) =>
      println("Result of " + dividend.get + "/"+ divisor.get +" is: " + v)
      Success(v)
    case Failure(e) =>
      println("You must've divided by zero or entered something that's not an Int. Try again!")
      println("Info from the exception: " + e.getMessage)
      divide
  }
}

An important property of Try shown in the above example is its ability to pipeline, or chain, operations, catching exceptions along the way. The flatMap and map combinators in the above example each essentially pass off either their successfully completed value, wrapped in the Success type for it to be further operated upon by the next combinator in the chain, or the exception wrapped in the Failure type usually to be simply passed on down the chain. Combinators such as recover and recoverWith are designed to provide some type of default behavior in the case of failure.

Note: only non-fatal exceptions are caught by the combinators on Try (see scala.util.control.NonFatal). Serious system errors, on the other hand, will be thrown.

Note:: all Try combinators will catch exceptions and return failure unless otherwise specified in the documentation.

Attributes

Companion: object
Source: Try.scala
Graph
Supertypes: trait Serializable

trait Product

trait Equals

class Object

trait Matchable

class Any
Show all
Known subtypes: class Failure[T]

class Success[T]

Members list

Type members

Classlikes

We need a whole WithFilter class to honor the "doesn't create a new collection" contract even though it seems unlikely to matter much in a collection with max size 1.

Attributes

Source: Try.scala
Supertypes: class Object

trait Matchable

class Any

Value members

Abstract methods

Applies the given partial function to the value from this Success or returns this if this is a Failure.

Attributes

Source: Try.scala

Inverts this Try.

Inverts this Try. If this is a Failure, returns its exception wrapped in a Success. If this is a Success, returns a Failure containing an UnsupportedOperationException.

Attributes

Source: Try.scala

Converts this to a Failure if the predicate is not satisfied.

Attributes

Source: Try.scala

Returns the given function applied to the value from this Success or returns this if this is a Failure.

Attributes

Source: Try.scala

Transforms a nested Try, ie, a Try of type Try[Try[T]], into an un-nested Try, ie, a Try of type Try[T].

Attributes

Source: Try.scala

Applies fa if this is a Failure or fb if this is a Success.

Applies fa if this is a Failure or fb if this is a Success. If fb is initially applied and throws an exception, then fa is applied with this exception.

Value parameters

fa: the function to apply if this is a Failure
fb: the function to apply if this is a Success

Attributes

Returns

the results of applying the function

Example

val result: Try[Int] = Try { string.toInt }
log(result.fold(
 ex => "Operation failed with " + ex,
 v => "Operation produced value: " + v
))

Source

Try.scala

Applies the given function f if this is a Success, otherwise returns Unit if this is a Failure.

Note: If f throws, then this method may throw an exception.

Attributes

Source: Try.scala

Returns the value from this Success or throws the exception if this is a Failure.

Attributes

Source: Try.scala

Returns the value from this Success or the given default argument if this is a Failure.

Note:: This will throw an exception if it is not a success and default throws an exception.

Attributes

Source: Try.scala

Returns true if the Try is a Failure, false otherwise.

Attributes

Source: Try.scala

Returns true if the Try is a Success, false otherwise.

Attributes

Source: Try.scala

Maps the given function to the value from this Success or returns this if this is a Failure.

Attributes

Source: Try.scala

Returns this Try if it's a Success or the given default argument if this is a Failure.

Attributes

Source: Try.scala

Applies the given function f if this is a Failure, otherwise returns this if this is a Success.

Applies the given function f if this is a Failure, otherwise returns this if this is a Success. This is like map for the exception.

Attributes

Source: Try.scala

Applies the given function f if this is a Failure, otherwise returns this if this is a Success.

Applies the given function f if this is a Failure, otherwise returns this if this is a Success. This is like flatMap for the exception.

Attributes

Source: Try.scala

Returns Left with Throwable if this is a Failure, otherwise returns Right with Success value.

Attributes

Source: Try.scala

Returns None if this is a Failure or a Some containing the value if this is a Success.

Attributes

Source: Try.scala

Completes this Try by applying the function f to this if this is of type Failure, or conversely, by applying s if this is a Success.

Attributes

Source: Try.scala

Concrete methods

Creates a non-strict filter, which eventually converts this to a Failure if the predicate is not satisfied.

Note: unlike filter, withFilter does not create a new Try. Instead, it restricts the domain of subsequent map, flatMap, foreach, and withFilter operations.

As Try is a one-element collection, this may be a bit overkill, but it's consistent with withFilter on Option and the other collections.

Value parameters

p: the predicate used to test elements.

Attributes

Returns: an object of class WithFilter, which supports map, flatMap, foreach, and withFilter operations. All these operations apply to those elements of this Try which satisfy the predicate p.
Source: Try.scala

Inherited methods

The name of the nth element of this product, 0-based.

The name of the nth element of this product, 0-based. In the default implementation, an empty string.

Value parameters

n: the index of the element name to return

Attributes

Returns: the name of the specified element
Throws: IndexOutOfBoundsException if the n is out of range(n < 0 || n >= productArity).
Inherited from:: Product
Source: Product.scala

An iterator over the names of all the elements of this product.

Attributes

Inherited from:: Product
Source: Product.scala

An iterator over all the elements of this product.

Attributes

Returns: in the default implementation, an Iterator[Any]
Inherited from:: Product
Source: Product.scala

A string used in the toString methods of derived classes.

A string used in the toString methods of derived classes. Implementations may override this method to prepend a string prefix to the result of toString methods.

Attributes

Returns: in the default implementation, the empty string
Inherited from:: Product
Source: Product.scala

Inherited and Abstract methods

Checks whether this instance can possibly equal that.

A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.

Value parameters

that: the value being probed for possible equality

Attributes

Returns: true if this instance can possibly equal that, otherwise false
Inherited from:: Equals
Source: Equals.scala

The size of this product.

Attributes

Returns: for a product A(x1, ..., xk), returns k
Inherited from:: Product
Source: Product.scala

The nth element of this product, 0-based.

The nth element of this product, 0-based. In other words, for a product A(x1, ..., xk), returns x(n+1) where 0 <= n < k.

Value parameters

n: the index of the element to return

Attributes

Returns: the element n elements after the first element
Throws: IndexOutOfBoundsException if the n is out of range(n < 0 || n >= productArity).
Inherited from:: Product
Source: Product.scala

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