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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Abstract Value Members
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abstract
def
eval[T](expr: blackbox.Context.Expr[T]): T
Takes a typed wrapper for a tree of type
Tand evaluates it to a value of typeT.Takes a typed wrapper for a tree of type
Tand 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 toduplicatethe 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
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final
def
!=(arg0: Any): Boolean
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final
def
##(): Int
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- def +(other: String): String
- def ->[B](y: B): (Evals, B)
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final
def
==(arg0: Any): Boolean
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final
def
asInstanceOf[T0]: T0
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def
clone(): AnyRef
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- protected[lang]
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- @throws( ... ) @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
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final
def
eq(arg0: AnyRef): Boolean
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def
equals(arg0: Any): Boolean
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def
finalize(): Unit
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- def formatted(fmtstr: String): String
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final
def
getClass(): Class[_]
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def
hashCode(): Int
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final
def
isInstanceOf[T0]: Boolean
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def
ne(arg0: AnyRef): Boolean
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final
def
notify(): Unit
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final
def
notifyAll(): Unit
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final
def
synchronized[T0](arg0: ⇒ T0): T0
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def
toString(): String
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final
def
wait(): Unit
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final
def
wait(arg0: Long, arg1: Int): Unit
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final
def
wait(arg0: Long): Unit
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