annotation
A base class for annotations.
A base class for classfile annotations.
A base class for classfile annotations. These are stored as Java annotations] in classfiles.
1.1, 2/02/2007
2.4
A base class for static annotations.
A base class for static annotations. These are available to the Scala type checker, even across different compilation units.
1.1, 2/02/2007
2.4
A marker for annotations that, when applied to a type, should be treated as a constraint on the annotated type.
A marker for annotations that, when applied to a type, should be treated as a constraint on the annotated type.
A proper constraint should restrict the type based only on information mentioned within the type. A Scala compiler can use this assumption to rewrite the contents of the constraint as necessary. To contrast, a type annotation whose meaning depends on the context where it is written down is not a proper constrained type, and this marker should not be applied. A Scala compiler will drop such annotations in cases where it would rewrite a type constraint.
1.1, 2007-11-5
2.6
An annotation that designates that an annottee should not be referred to after type checking (which includes macro expansion).
An annotation that designates that an annottee should not be referred to after type checking (which includes macro expansion).
Examples of potential use: 1) The annottee can only appear in the arguments of some other macro that will eliminate it from the AST during expansion. 2) The annottee is a macro and should have been expanded away, so if hasn't, something wrong has happened. (Comes in handy to provide better support for new macro flavors, e.g. macro annotations, that can't be expanded by the vanilla compiler).
2.11.0
An annotation for methods whose bodies may be excluded from compiler-generated bytecode.
An annotation for methods whose bodies may be excluded from compiler-generated bytecode.
Behavior is influenced by passing -Xelide-below <arg> to scalac.
Calls to methods marked elidable (as well as the method body) will
be omitted from generated code if the priority given the annotation
is lower than that given on the command line.
@elidable(123) // annotation priority scalac -Xelide-below 456 // command line priority
The method call will be replaced with an expression which depends on the type of the elided expression. In decreasing order of precedence:
Unit () Boolean false T <: AnyVal 0 T >: Null null T >: Nothing Predef.???
Complete example:
import scala.annotation._, elidable._ object Test extends App { def expensiveComputation(): Int = { Thread.sleep(1000) ; 172 } @elidable(WARNING) def warning(msg: String) = println(msg) @elidable(FINE) def debug(msg: String) = println(msg) @elidable(FINE) def computedValue = expensiveComputation() warning("Warning! Danger! Warning!") debug("Debug! Danger! Debug!") println("I computed a value: " + computedValue) } % scalac example.scala && scala Test Warning! Danger! Warning! Debug! Danger! Debug! I computed a value: 172 // INFO lies between WARNING and FINE % scalac -Xelide-below INFO example.scala && scala Test Warning! Danger! Warning! I computed a value: 0
2.8
To customize the error message that's emitted when an implicit of type C[T1,..., TN] cannot be found, annotate the class C with @implicitNotFound.
To customize the error message that's emitted when an implicit of type C[T1,..., TN] cannot be found, annotate the class C with @implicitNotFound. Assuming C has type parameters X1,..., XN, the error message will be the result of replacing all occurrences of ${Xi} in the string msg with the string representation of the corresponding type argument Ti. *
2.8.1
If this annotation is present on a method or its enclosing class, the strictfp flag will be emitted.
If this annotation is present on a method or its enclosing class, the strictfp flag will be emitted.
2.9
2.9
An annotation to be applied to a match expression.
An annotation to be applied to a match expression. If present, the compiler will verify that the match has been compiled to a tableswitch or lookupswitch and issue an error if it instead compiles into a series of conditional expressions. Example usage:
val Constant = 'Q' def tokenMe(ch: Char) = (ch: @switch) match { case ' ' | '\t' | '\n' => 1 case 'A' | 'Z' | '$' => 2 case '5' | Constant => 3 // a non-literal may prevent switch generation: this would not compile case _ => 4 }
Note: for pattern matches with one or two cases, the compiler generates jump instructions.
Annotating such a match with @switch does not issue any warning.
2.8
A method annotation which verifies that the method will be compiled with tail call optimization.
A method annotation which verifies that the method will be compiled with tail call optimization.
If it is present, the compiler will issue an error if the method cannot be optimized into a loop.
2.8
A method annotation which suppresses the creation of additional specialized forms based on enclosing specialized type parameters.
A method annotation which suppresses the creation of additional specialized forms based on enclosing specialized type parameters.
2.10
A method annotation which instructs the compiler to generate a Java varargs-style forwarder method for interop.
A method annotation which instructs the compiler to generate a Java varargs-style forwarder method for interop. This annotation can only be applied to methods with repeated parameters.
2.9
This useless appearing code was necessary to allow people to use named constants for the elidable annotation.
This useless appearing code was necessary to allow people to use named constants for the elidable annotation. This is what it takes to convince the compiler to fold the constants: otherwise when it's time to check an elision level it's staring at a tree like
(Select(Level, Select(FINEST, Apply(intValue, Nil))))
instead of the number 300.
2.8
When defining a field, the Scala compiler creates up to four accessors
for it: a getter, a setter, and if the field is annotated with
@BeanProperty, a bean getter and a bean setter.
When defining a field, the Scala compiler creates up to four accessors
for it: a getter, a setter, and if the field is annotated with
@BeanProperty, a bean getter and a bean setter.
For instance in the following class definition
class C(@myAnnot @BeanProperty var c: Int)
there are six entities which can carry the annotation @myAnnot: the
constructor parameter, the generated field and the four accessors.
By default, annotations on (val-, var- or plain) constructor parameters
end up on the parameter, not on any other entity. Annotations on fields
by default only end up on the field.
The meta-annotations in package scala.annotation.meta are used
to control where annotations on fields and class parameters are copied.
This is done by annotating either the annotation type or the annotation
class with one or several of the meta-annotations in this package.
The target meta-annotations can be put on the annotation type when
instantiating the annotation. In the following example, the annotation
@Id will be added only to the bean getter getX.
import javax.persistence.Id class A { @(Id @beanGetter) @BeanProperty val x = 0 }
In order to annotate the field as well, the meta-annotation @field
would need to be added.
The syntax can be improved using a type alias:
object ScalaJPA { type Id = javax.persistence.Id @beanGetter } import ScalaJPA.Id class A { @Id @BeanProperty val x = 0 }
For annotations defined in Scala, a default target can be specified in the annotation class itself, for example
@getter class myAnnotation extends Annotation
This only changes the default target for the annotation myAnnotation.
When instantiating the annotation, the target can still be specified
as described in the last section.
A base class for annotations. Annotations extending this class directly are not preserved for the Scala type checker and are also not stored as Java annotations in classfiles. To enable either or both of these, one needs to inherit from scala.annotation.StaticAnnotation or/and scala.annotation.ClassfileAnnotation.
1.1, 2/02/2007
2.4