Using

object Using

A utility for performing automatic resource management. It can be used to perform an operation using resources, after which it releases the resources in reverse order of their creation.

Usage

There are multiple ways to automatically manage resources with Using. If you only need to manage a single resource, the apply method is easiest; it wraps the resource opening, operation, and resource releasing in a Try.

Example:

import java.io.{BufferedReader, FileReader} import scala.util.{Try, Using} val lines: Try[Seq[String]] = Using(new BufferedReader(new FileReader("file.txt"))) { reader => Iterator.continually(reader.readLine()).takeWhile(_ != null).toSeq }

If you need to manage multiple resources, Using.Manager should be used. It allows the managing of arbitrarily many resources, whose creation, use, and release are all wrapped in a Try.

Example:

import java.io.{BufferedReader, FileReader} import scala.util.{Try, Using} val lines: Try[Seq[String]] = Using.Manager { use => val r1 = use(new BufferedReader(new FileReader("file1.txt"))) val r2 = use(new BufferedReader(new FileReader("file2.txt"))) val r3 = use(new BufferedReader(new FileReader("file3.txt"))) val r4 = use(new BufferedReader(new FileReader("file4.txt"))) // use your resources here def lines(reader: BufferedReader): Iterator[String] = Iterator.continually(reader.readLine()).takeWhile(_ != null) (lines(r1) ++ lines(r2) ++ lines(r3) ++ lines(r4)).toList }

If you wish to avoid wrapping management and operations in a Try, you can use Using.resource, which throws any exceptions that occur.

Example:

import java.io.{BufferedReader, FileReader} import scala.util.Using val lines: Seq[String] = Using.resource(new BufferedReader(new FileReader("file.txt"))) { reader => Iterator.continually(reader.readLine()).takeWhile(_ != null).toSeq }

Suppression Behavior

If two exceptions are thrown (e.g., by an operation and closing a resource), one of them is re-thrown, and the other is added to it as a suppressed exception. If the two exceptions are of different 'severities' (see below), the one of a higher severity is re-thrown, and the one of a lower severity is added to it as a suppressed exception. If the two exceptions are of the same severity, the one thrown first is re-thrown, and the one thrown second is added to it as a suppressed exception. If an exception is a ControlThrowable, or if it does not support suppression (see Throwable's constructor with an enableSuppression parameter), an exception that would have been suppressed is instead discarded.

Exceptions are ranked from highest to lowest severity as follows:

  • java.lang.VirtualMachineError

  • java.lang.LinkageError

  • java.lang.InterruptedException and java.lang.ThreadDeath

  • fatal exceptions, excluding scala.util.control.ControlThrowable

  • scala.util.control.ControlThrowable

  • all other exceptions

When more than two exceptions are thrown, the first two are combined and re-thrown as described above, and each successive exception thrown is combined as it is thrown.

class Object
trait Matchable
class Any

Type members

Classlikes

final class Manager

A resource manager.

Resources can be registered with the manager by calling acquire; such resources will be released in reverse order of their acquisition when the manager is closed, regardless of any exceptions thrown during use.

See the main doc for Using for full details of suppression behavior.

Note

It is recommended for API designers to require an implicit Manager for the creation of custom resources, and to call acquire during those resources' construction. Doing so guarantees that the resource must be automatically managed, and makes it impossible to forget to do so. Example:

class SafeFileReader(file: File)(implicit manager: Using.Manager) extends BufferedReader(new FileReader(file)) { def this(fileName: String)(implicit manager: Using.Manager) = this(new File(fileName)) manager.acquire(this) }
Companion
object
Source
Using.scala
object Manager
Companion
class
Source
Using.scala
trait Releasable[-R]

A type class describing how to release a particular type of resource.

A resource is anything which needs to be released, closed, or otherwise cleaned up in some way after it is finished being used, and for which waiting for the object's garbage collection to be cleaned up would be unacceptable. For example, an instance of java.io.OutputStream would be considered a resource, because it is important to close the stream after it is finished being used.

An instance of Releasable is needed in order to automatically manage a resource with Using. An implicit instance is provided for all types extending java.lang.AutoCloseable.

Type Params
R

the type of the resource

Companion
object
Source
Using.scala
object Releasable
Companion
class
Source
Using.scala

Value members

Concrete methods

def apply[R, A](resource: => R)(f: R => A)(`evidence$1`: Releasable[R]): Try[A]

Performs an operation using a resource, and then releases the resource, even if the operation throws an exception.

See the main doc for Using for full details of suppression behavior.

Returns

a Try containing an exception if one or more were thrown, or the result of the operation if no exceptions were thrown

Source
Using.scala
def resource[R, A](resource: R)(body: R => A)(releasable: Releasable[R]): A

Performs an operation using a resource, and then releases the resource, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.

See the main doc for Using for full details of suppression behavior.

Type Params
A

the return type of the operation

R

the type of the resource

Value Params
body

the operation to perform with the resource

resource

the resource

Returns

the result of the operation, if neither the operation nor releasing the resource throws

Source
Using.scala
def resources[R1, R2, A](resource1: R1, resource2: => R2)(body: (R1, R2) => A)(`evidence$2`: Releasable[R1], `evidence$3`: Releasable[R2]): A

Performs an operation using two resources, and then releases the resources in reverse order, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.

See the main doc for Using for full details of suppression behavior.

Type Params
A

the return type of the operation

R1

the type of the first resource

R2

the type of the second resource

Value Params
body

the operation to perform using the resources

resource1

the first resource

resource2

the second resource

Returns

the result of the operation, if neither the operation nor releasing the resources throws

Source
Using.scala
def resources[R1, R2, R3, A](resource1: R1, resource2: => R2, resource3: => R3)(body: (R1, R2, R3) => A)(`evidence$4`: Releasable[R1], `evidence$5`: Releasable[R2], `evidence$6`: Releasable[R3]): A

Performs an operation using three resources, and then releases the resources in reverse order, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.

See the main doc for Using for full details of suppression behavior.

Type Params
A

the return type of the operation

R1

the type of the first resource

R2

the type of the second resource

R3

the type of the third resource

Value Params
body

the operation to perform using the resources

resource1

the first resource

resource2

the second resource

resource3

the third resource

Returns

the result of the operation, if neither the operation nor releasing the resources throws

Source
Using.scala
def resources[R1, R2, R3, R4, A](resource1: R1, resource2: => R2, resource3: => R3, resource4: => R4)(body: (R1, R2, R3, R4) => A)(`evidence$7`: Releasable[R1], `evidence$8`: Releasable[R2], `evidence$9`: Releasable[R3], `evidence$10`: Releasable[R4]): A

Performs an operation using four resources, and then releases the resources in reverse order, even if the operation throws an exception. This method behaves similarly to Java's try-with-resources.

See the main doc for Using for full details of suppression behavior.

Type Params
A

the return type of the operation

R1

the type of the first resource

R2

the type of the second resource

R3

the type of the third resource

R4

the type of the fourth resource

Value Params
body

the operation to perform using the resources

resource1

the first resource

resource2

the second resource

resource3

the third resource

resource4

the fourth resource

Returns

the result of the operation, if neither the operation nor releasing the resources throws

Source
Using.scala