AnyVal is the root class of all value types, which describe values
not implemented as objects in the underlying host system. Value classes
are specified in Scala Language Specification, section 12.2.
The standard implementation includes nine AnyVal subtypes:
Prior to Scala 2.10, AnyVal was a sealed trait. Beginning with Scala 2.10,
however, it is possible to define a subclass of AnyVal called a user-defined value class
which is treated specially by the compiler. Properly-defined user value classes provide a way
to improve performance on user-defined types by avoiding object allocation at runtime, and by
replacing virtual method invocations with static method invocations.
User-defined value classes which avoid object allocation...
must have a single, public val parameter that is the underlying runtime representation.
can define defs, but no vals, vars, or nested traitss, classes or objects.
typically extend no other trait apart from AnyVal.
cannot be used in type tests or pattern matching.
may not override equals or hashCode methods.
A minimal example:
class Wrapper(val underlying: Int) extendsAnyVal {
def foo: Wrapper = new Wrapper(underlying * 19)
}
It's important to note that user-defined value classes are limited, and in some circumstances,
still must allocate a value class instance at runtime. These limitations and circumstances are
explained in greater detail in the Value Classes Guide
as well as in SIP-15: Value Classes,
the Scala Improvement Proposal.
AnyValis the root class of all value types, which describe values not implemented as objects in the underlying host system. Value classes are specified in Scala Language Specification, section 12.2.The standard implementation includes nine
AnyValsubtypes:scala.Double, scala.Float, scala.Long, scala.Int, scala.Char, scala.Short, and scala.Byte are the numeric value types.
scala.Unit and scala.Boolean are the non-numeric value types.
Other groupings:
Prior to Scala 2.10,
AnyValwas a sealed trait. Beginning with Scala 2.10, however, it is possible to define a subclass ofAnyValcalled a user-defined value class which is treated specially by the compiler. Properly-defined user value classes provide a way to improve performance on user-defined types by avoiding object allocation at runtime, and by replacing virtual method invocations with static method invocations.User-defined value classes which avoid object allocation...
valparameter that is the underlying runtime representation.defs, but novals,vars, or nestedtraitss,classes orobjects.AnyVal.equalsorhashCodemethods.A minimal example:
It's important to note that user-defined value classes are limited, and in some circumstances, still must allocate a value class instance at runtime. These limitations and circumstances are explained in greater detail in the Value Classes Guide as well as in SIP-15: Value Classes, the Scala Improvement Proposal.