Scala Reflection Library2.13.17 < Back
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# Packages

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    root
-  package scala
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    root
-  package reflect
  Definition Classes
    scala
-  package macros

  EXPERIMENTAL

  EXPERIMENTAL

  The base package for Scala macros.

  Macros are functions that are called by the compiler during compilation. Within these functions the programmer has access to compiler APIs. For example, it is possible to generate, analyze and typecheck code.

  See the Macros Guide on how to get started with Scala macros.

  Definition Classes
    reflect
-  package blackbox
  Definition Classes
    macros
-  package whitebox
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    macros
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t

scala.reflect.macros

# Evals

###

#### trait Evals extends AnyRef

EXPERIMENTAL

A slice of the Scala macros context that provides a facility to evaluate trees.

Self Type
  blackbox.Context
Source
  Evals.scala

Linear Supertypes
AnyRef, Any
Known Subclasses
Context, Context
Type Hierarchy

Ordering

1. Alphabetic
2. By Inheritance

Inherited

1. Evals
2. AnyRef
3. Any

Implicitly

1. by any2stringadd
2. by StringFormat
3. by Ensuring
4. by ArrowAssoc

1. Hide All
2. Show All

Visibility

1. Public
2. Protected

### Abstract Value Members

1.  abstract def eval[T](expr: blackbox.Context.Expr[T]): T

   Takes a typed wrapper for a tree of type `T` and evaluates it to a value of type `T`.

   Takes a typed wrapper for a tree of type `T` and evaluates it to a value of type `T`.

   Can be used to perform compile-time computations on macro arguments to the extent permitted by the shape of the arguments.

   Known issues: because of https://github.com/scala/bug/issues/5748 trees being evaluated first need to undergo `untypecheck`. Resetting symbols and types mutates the tree in place, therefore the conventional approach is to `duplicate` the tree first.

       scala> def impl(c: Context)(x: c.Expr[String]) = {
            | val x1 = c.Expr[String](c.untypecheck(x.tree.duplicate))
            | println(s"compile-time value is: ${c.eval(x1)}")
            | x
            | }
       impl: (c: Context)(x: c.Expr[String])c.Expr[String]

       scala> def test(x: String) = macro impl
       test: (x: String)String

       scala> test("x")
       compile-time value is: x
       res0: String = x

       scala> test("x" + "y")
       compile-time value is: xy
       res1: String = xy

       scala> val x = "x"
       x: String = x

       scala> test(x + "y")
       compile-time value is: xy
       res2: String = xy

       scala> { val x = "x"; test(x + "y") }
       error: exception during macro expansion:
       scala.tools.reflect.ToolBoxError: reflective compilation failed

   Note that in the last case evaluation has failed, because the argument of a macro refers to a runtime value `x`, which is unknown at compile time.

### Concrete Value Members

1.  final def !=(arg0: Any): Boolean
   Definition Classes
     AnyRef → Any
2.  final def ##: Int
   Definition Classes
     AnyRef → Any
3.  def +(other: String): String
   Implicit
     This member is added by an implicit conversion from Evals toany2stringadd[Evals] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd
4.  def ->[B](y: B): (Evals, B)
   Implicit
     This member is added by an implicit conversion from Evals toArrowAssoc[Evals] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @inline()
5.  final def ==(arg0: Any): Boolean
   Definition Classes
     AnyRef → Any
6.  final def asInstanceOf[T0]: T0
   Definition Classes
     Any
7.  def clone(): AnyRef
   Attributes
     protected[lang]
   Definition Classes
     AnyRef
   Annotations
     @throws(classOf[java.lang.CloneNotSupportedException]) @native()
8.  def ensuring(cond: (Evals) => Boolean, msg: => Any): Evals
   Implicit
     This member is added by an implicit conversion from Evals toEnsuring[Evals] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
9.  def ensuring(cond: (Evals) => Boolean): Evals
   Implicit
     This member is added by an implicit conversion from Evals toEnsuring[Evals] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
10.  def ensuring(cond: Boolean, msg: => Any): Evals
    Implicit
      This member is added by an implicit conversion from Evals toEnsuring[Evals] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
11.  def ensuring(cond: Boolean): Evals
    Implicit
      This member is added by an implicit conversion from Evals toEnsuring[Evals] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
12.  final def eq(arg0: AnyRef): Boolean
    Definition Classes
      AnyRef
13.  def equals(arg0: AnyRef): Boolean
    Definition Classes
      AnyRef → Any
14.  def finalize(): Unit
    Attributes
      protected[lang]
    Definition Classes
      AnyRef
    Annotations
      @throws(classOf[java.lang.Throwable])
15.  final def getClass(): Class[_ <: AnyRef]
    Definition Classes
      AnyRef → Any
    Annotations
      @native()
16.  def hashCode(): Int
    Definition Classes
      AnyRef → Any
    Annotations
      @native()
17.  final def isInstanceOf[T0]: Boolean
    Definition Classes
      Any
18.  final def ne(arg0: AnyRef): Boolean
    Definition Classes
      AnyRef
19.  final def notify(): Unit
    Definition Classes
      AnyRef
    Annotations
      @native()
20.  final def notifyAll(): Unit
    Definition Classes
      AnyRef
    Annotations
      @native()
21.  final def synchronized[T0](arg0: => T0): T0
    Definition Classes
      AnyRef
22.  def toString(): String
    Definition Classes
      AnyRef → Any
23.  final def wait(): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws(classOf[java.lang.InterruptedException])
24.  final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws(classOf[java.lang.InterruptedException])
25.  final def wait(arg0: Long): Unit
    Definition Classes
      AnyRef
    Annotations
      @throws(classOf[java.lang.InterruptedException]) @native()

### Deprecated Value Members

1.  def formatted(fmtstr: String): String
   Implicit
     This member is added by an implicit conversion from Evals toStringFormat[Evals] performed by method StringFormat in scala.Predef.
   Definition Classes
     StringFormat
   Annotations
     @deprecated @inline()
   Deprecated

     (Since version 2.12.16) Use `formatString.format(value)` instead of `value.formatted(formatString)`, or use the `f""` string interpolator. In Java 15 and later, `formatted` resolves to the new method in String which has reversed parameters.

2.  def →[B](y: B): (Evals, B)
   Implicit
     This member is added by an implicit conversion from Evals toArrowAssoc[Evals] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @deprecated
   Deprecated

     (Since version 2.13.0) Use `->` instead. If you still wish to display it as one character, consider using a font with programming ligatures such as Fira Code.

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion any2stringadd fromEvals to any2stringadd[Evals]

### Inherited by implicit conversion StringFormat fromEvals to StringFormat[Evals]

### Inherited by implicit conversion Ensuring fromEvals to Ensuring[Evals]

### Inherited by implicit conversion ArrowAssoc fromEvals to ArrowAssoc[Evals]

### Ungrouped