MbReflection

The MiniboxingReflection object allows reflecting on the type parameters of miniboxed classes. For example, given class C[@miniboxed T], reflection can determine at run-time whether a type parameter is miniboxed, its instantiation and what type is used to store this value. These methods do not incur any overhead, since they are compiled away by the miniboxing plugin.

Let's see an example:

scala> import MbReflection._
import MbReflection._

scala> class C[@miniboxed T] {
     |   override def toString: String =
     |     s"C[T = ${reifiedType[T]}, miniboxed into a ${storageType[T]}]"
     | }
defined class C

scala> new C[Int]
res4: C[Int] = C[T = int, miniboxed into a long]

scala> new C[Unit]
res5: C[Unit] = C[T = unit, miniboxed into a long]

scala> new C[Float]
res6: C[Float] = C[T = float, miniboxed into a double]

Yet, it's still possible to instantiate the class in an erased context, leading to suboptimal storage. Still, the miniboxing plugin will slap you on the wrist for doing so, and reflection will tell you you're doing it wrong:

scala> def newC[T] = new C[T]
<console>:11: warning: The following code could benefit from miniboxing
specialization if the type parameter T of method newC would be marked
as "@miniboxed T" (it would be used to instantiate miniboxed type
parameter T of class C)
       def newC[T] = new C[T]
                     ^
newC: [T]=> C[T]

scala> newC[Int]
<console>:13: warning: The method newC would benefit from miniboxing
type parameter T, since it is instantiated by a primitive type.
              newC[Int]
                  ^
 res3: C[Int] = C[T = reference, miniboxed into a reference]

Finally, there's a good use case for this, if the class is always supposed to be miniboxed:

scala> class D[@miniboxed T] {
     |   assert(isMiniboxed[T], "Idiot!")
     | }
define class D

scala> new D[String]
java.lang.AssertionError: assertion failed: Idiot!
  at scala.Predef$.assert(Predef.scala:165)
  ... 34 elided

The "isMiniboxed" method is also partially evaluated away by the compiler:

scala> def foo[@miniboxed T]: Unit = {
     |   if (isMiniboxed[T])
     |     println("foo[miniboxed]")
     |   else
     |     println("foo[reference]")
     | }
foo: [T]=> Unit

scala> foo[Byte]
foo[miniboxed]

In the low-level bytecode you will have:

def foo(): Unit = println("foo[reference]")
def foo_J(...): Unit = println("foo[miniboxed]")
def foo_D(...): Unit = println("foo[miniboxed]")

So there is 0 overhead in using the isMiniboxed method. Still, reifiedType and storageType are not partially evaluated and do incur a small overhead.

Linear Supertypes

AnyRef, Any

Value Members

final def !=(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def ##(): Int

Definition Classes
AnyRef → Any
final def ==(arg0: Any): Boolean

Definition Classes
AnyRef → Any
object SimpleConv
object SimpleType extends Enumeration
final def asInstanceOf[T0]: T0

Definition Classes
Any
def clone(): AnyRef

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( ... )
final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef
def equals(arg0: Any): Boolean

Definition Classes
AnyRef → Any
def finalize(): Unit

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
final def getClass(): Class[_]

Definition Classes
AnyRef → Any
def hashCode(): Int

Definition Classes
AnyRef → Any
final def isInstanceOf[T0]: Boolean

Definition Classes
Any
def isMiniboxed[T]: Boolean

Is this type parameter miniboxed?
final def ne(arg0: AnyRef): Boolean

Definition Classes
AnyRef
final def notify(): Unit

Definition Classes
AnyRef
final def notifyAll(): Unit

Definition Classes
AnyRef
def reifiedType[T]: SimpleType

If miniboxed, what is the actual type of a type parameter? It can be any of the scala miniboxing types.
def storageType[T]: SimpleType

If miniboxed, what is the storage type of a type parameter?
If miniboxed, what is the storage type of a type parameter?
The storage type of a miniboxed type parameter can be one of the following three types: * Object for instantiations with AnyRef-based types, erased generic types and value classes * Long for instantiations with Unit, Boolean, Byte, Char, Short, Int and Long * Double for instantiations with Float and Double
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
def toString(): String

Definition Classes
AnyRef → Any
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

Definition Classes
AnyRef
Annotations
@throws( ... )

Related Doc: package scala

object MbReflection

Value Members

final def !=(arg0: Any): Boolean

final def ##(): Int

final def ==(arg0: Any): Boolean

object SimpleConv

object SimpleType extends Enumeration

final def asInstanceOf[T0]: T0

def clone(): AnyRef

final def eq(arg0: AnyRef): Boolean

def equals(arg0: Any): Boolean

def finalize(): Unit

final def getClass(): Class[_]

def hashCode(): Int

final def isInstanceOf[T0]: Boolean

def isMiniboxed[T]: Boolean

final def ne(arg0: AnyRef): Boolean

final def notify(): Unit

final def notifyAll(): Unit

def reifiedType[T]: SimpleType

def storageType[T]: SimpleType

final def synchronized[T0](arg0: ⇒ T0): T0

def toString(): String

final def wait(): Unit

final def wait(arg0: Long, arg1: Int): Unit

final def wait(arg0: Long): Unit

Inherited from AnyRef

Inherited from Any

Ungrouped