Packages

  • package root

    This is the documentation for the Scala standard library.

    This is the documentation for the Scala standard library.

    Package structure

    The scala package contains core types like Int, Float, Array or Option which are accessible in all Scala compilation units without explicit qualification or imports.

    Notable packages include:

    Other 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 for scala.collection.immutable.List.

    Other aliases refer to classes provided by the underlying platform. For example, on the JVM, String is an alias for java.lang.String.

    Definition Classes
    root
  • package scala

    Core Scala types.

    Core Scala types. They are always available without an explicit import.

    Definition Classes
    root
  • object Predef extends LowPriorityImplicits

    The Predef object provides definitions that are accessible in all Scala compilation units without explicit qualification.

    The Predef object provides definitions that are accessible in all Scala compilation units without explicit qualification.

    Commonly Used Types

    Predef provides type aliases for types which are commonly used, such as the immutable collection types scala.collection.immutable.Map, scala.collection.immutable.Set, and the scala.collection.immutable.List constructors (scala.collection.immutable.:: and scala.collection.immutable.Nil).

    Console Output

    For basic console output, Predef provides convenience methods print and println, which are aliases of the methods in the object scala.Console.

    Assertions

    A set of assert functions are provided for use as a way to document and dynamically check invariants in code. Invocations of assert can be elided at compile time by providing the command line option -Xdisable-assertions, which raises -Xelide-below above elidable.ASSERTION, to the scalac command.

    Variants of assert intended for use with static analysis tools are also provided: assume, require and ensuring. require and ensuring are intended for use as a means of design-by-contract style specification of pre- and post-conditions on functions, with the intention that these specifications could be consumed by a static analysis tool. For instance,

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

    The declaration of addNaturals states that the list of integers passed should only contain natural numbers (i.e. non-negative), and that the result returned will also be natural. require is distinct from assert in that if the condition fails, then the caller of the function is to blame rather than a logical error having been made within addNaturals itself. ensuring is a form of assert that declares the guarantee the function is providing with regards to its return value.

    Implicit Conversions

    A number of commonly applied implicit conversions are also defined here, and in the parent type scala.LowPriorityImplicits. Implicit conversions are provided for the "widening" of numeric values, for instance, converting a Short value to a Long value as required, and to add additional higher-order functions to Array values. These are described in more detail in the documentation of scala.Array.

    Definition Classes
    scala
  • <:<
  • =:=
  • ArrayCharSequence
  • ArrowAssoc
  • DummyImplicit
  • Ensuring
  • SeqCharSequence
  • StringFormat
  • any2stringadd
c

scala.Predef

Ensuring

implicit final class Ensuring[A] extends AnyVal

Source
Predef.scala
Linear Supertypes
Type Hierarchy
Ordering
  1. Alphabetic
  2. By Inheritance
Inherited
  1. Ensuring
  2. AnyVal
  3. Any
Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by ArrowAssoc
  4. by any2stringadd
  5. by StringFormat
  6. by ArrowAssoc
  1. Hide All
  2. Show All
Visibility
  1. Public
  2. All

Instance Constructors

  1. new Ensuring(self: A)

Value Members

  1. final def !=(arg0: Any): Boolean

    Test two objects for inequality.

    Test two objects for inequality.

    returns

    true if !(this == that), false otherwise.

    Definition Classes
    Any
  2. final def ##(): Int

    Equivalent to x.hashCode except for boxed numeric types and null.

    Equivalent to x.hashCode except for boxed numeric types and null. 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. For null returns a hashcode where null.hashCode throws a NullPointerException.

    returns

    a hash value consistent with ==

    Definition Classes
    Any
  3. final def ==(arg0: Any): Boolean

    Test two objects for equality.

    Test two objects for equality. The expression x == that is equivalent to if (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
    Any
  4. 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 a ClassCastException at runtime, while the expression List(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

    ClassCastException if the receiver object is not an instance of the erasure of type T0.

  5. def ensuring(cond: (A) ⇒ Boolean, msg: ⇒ Any): A
  6. def ensuring(cond: (A) ⇒ Boolean): A
  7. def ensuring(cond: Boolean, msg: ⇒ Any): A
  8. def ensuring(cond: Boolean): A
  9. def getClass(): Class[_ <: AnyVal]

    Returns the runtime class representation of the object.

    Returns the runtime class representation of the object.

    returns

    a class object corresponding to the runtime type of the receiver.

    Definition Classes
    AnyValAny
  10. 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 return false, while the expression List(1).isInstanceOf[List[String]] will return true. 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

    true if the receiver object is an instance of erasure of type T0; false otherwise.

    Definition Classes
    Any
  11. def toString(): java.lang.String

    Returns a string representation of the object.

    Returns a string representation of the object.

    The default representation is platform dependent.

    returns

    a string representation of the object.

    Definition Classes
    Any

Shadowed Implicit Value Members

  1. def +(other: String): String
    Implicit
    This member is added by an implicit conversion from Ensuring[A] toany2stringadd[Ensuring[A]] performed by method any2stringadd in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (ensuring: any2stringadd[Ensuring[A]]).+(other)
    Definition Classes
    any2stringadd
  2. def +(other: String): String
    Implicit
    This member is added by an implicit conversion from Ensuring[A] toany2stringadd[Ensuring[A]] performed by method any2stringadd in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (ensuring: any2stringadd[Ensuring[A]]).+(other)
    Definition Classes
    any2stringadd
  3. def ->[B](y: B): (Ensuring[A], B)
    Implicit
    This member is added by an implicit conversion from Ensuring[A] toArrowAssoc[Ensuring[A]] performed by method ArrowAssoc in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (ensuring: ArrowAssoc[Ensuring[A]]).->(y)
    Definition Classes
    ArrowAssoc
    Annotations
    @inline()
  4. def ->[B](y: B): (Ensuring[A], B)
    Implicit
    This member is added by an implicit conversion from Ensuring[A] toArrowAssoc[Ensuring[A]] performed by method ArrowAssoc in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (ensuring: ArrowAssoc[Ensuring[A]]).->(y)
    Definition Classes
    ArrowAssoc
    Annotations
    @inline()
  5. 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 for String.format (@see java.lang.String.format).

    Implicit
    This member is added by an implicit conversion from Ensuring[A] toStringFormat[Ensuring[A]] performed by method StringFormat in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (ensuring: StringFormat[Ensuring[A]]).formatted(fmtstr)
    Definition Classes
    StringFormat
    Annotations
    @inline()
  6. 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 for String.format (@see java.lang.String.format).

    Implicit
    This member is added by an implicit conversion from Ensuring[A] toStringFormat[Ensuring[A]] performed by method StringFormat in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (ensuring: StringFormat[Ensuring[A]]).formatted(fmtstr)
    Definition Classes
    StringFormat
    Annotations
    @inline()
  7. def [B](y: B): (Ensuring[A], B)
    Implicit
    This member is added by an implicit conversion from Ensuring[A] toArrowAssoc[Ensuring[A]] performed by method ArrowAssoc in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (ensuring: ArrowAssoc[Ensuring[A]]).→(y)
    Definition Classes
    ArrowAssoc
  8. def [B](y: B): (Ensuring[A], B)
    Implicit
    This member is added by an implicit conversion from Ensuring[A] toArrowAssoc[Ensuring[A]] performed by method ArrowAssoc in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (ensuring: ArrowAssoc[Ensuring[A]]).→(y)
    Definition Classes
    ArrowAssoc

Inherited from AnyVal

Inherited from Any

Inherited by implicit conversion any2stringadd fromEnsuring[A] to any2stringadd[Ensuring[A]]

Inherited by implicit conversion StringFormat fromEnsuring[A] to StringFormat[Ensuring[A]]

Inherited by implicit conversion ArrowAssoc fromEnsuring[A] to ArrowAssoc[Ensuring[A]]

Inherited by implicit conversion any2stringadd fromEnsuring[A] to any2stringadd[Ensuring[A]]

Inherited by implicit conversion StringFormat fromEnsuring[A] to StringFormat[Ensuring[A]]

Inherited by implicit conversion ArrowAssoc fromEnsuring[A] to ArrowAssoc[Ensuring[A]]

Ungrouped