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
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- Evals
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- Any
- by any2stringadd
- by StringFormat
- by Ensuring
- by ArrowAssoc
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Abstract Value Members
- 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 typeT
.Takes a typed wrapper for a tree of type
T
and evaluates it to a value of typeT
.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 toduplicate
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
- final def !=(arg0: Any): Boolean
- Definition Classes
- AnyRef → Any
- final def ##: Int
- Definition Classes
- AnyRef → Any
- def +(other: String): String
- def ->[B](y: B): (Evals, B)
- final def ==(arg0: Any): Boolean
- Definition Classes
- AnyRef → Any
- final def asInstanceOf[T0]: T0
- Definition Classes
- Any
- def clone(): AnyRef
- Attributes
- protected[lang]
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.CloneNotSupportedException]) @native()
- def ensuring(cond: (Evals) => Boolean, msg: => Any): Evals
- def ensuring(cond: (Evals) => Boolean): Evals
- def ensuring(cond: Boolean, msg: => Any): Evals
- def ensuring(cond: Boolean): Evals
- final def eq(arg0: AnyRef): Boolean
- Definition Classes
- AnyRef
- def equals(arg0: AnyRef): Boolean
- Definition Classes
- AnyRef → Any
- def finalize(): Unit
- Attributes
- protected[lang]
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.Throwable])
- def formatted(fmtstr: String): String
- final def getClass(): Class[_ <: AnyRef]
- Definition Classes
- AnyRef → Any
- Annotations
- @native()
- def hashCode(): Int
- Definition Classes
- AnyRef → Any
- Annotations
- @native()
- final def isInstanceOf[T0]: Boolean
- Definition Classes
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- final def ne(arg0: AnyRef): Boolean
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- final def notify(): Unit
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- @native()
- final def notifyAll(): Unit
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- @native()
- final def synchronized[T0](arg0: => T0): T0
- Definition Classes
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- def toString(): String
- Definition Classes
- AnyRef → Any
- final def wait(): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
- final def wait(arg0: Long, arg1: Int): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
- final def wait(arg0: Long): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException]) @native()
Deprecated Value Members
- 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.