可变长度的scala字符串插值

我使用scala f字符串插值器，如下所示：

def format(id: Int) = f"A$id%04d"
format(21)  // A0021

但是，我希望能够一次性地定义一个长度（在固定为4之前），并获得一个函数，它将使用该长度格式化字符串。 因此，与其

def format(length: Int, id: Int) = ???
f(5, 21)       // A00021

我想要这个：

def format(length: Int)(id: Int) = ???
val f = format(5)
f(21)       // A00021

如何使用scala f插值器或其他工具实现这一点

更新

我没有在运行时寻找涉及编译器的解决方案，但我很欣赏som snytt的回答。根据他的回答，这里有一个可行的解决方案：

import scala.tools.reflect._,scala.reflect.runtime._,universe._

def defFormat(length: Int): Int => String = {
  val code = raw"""(i: Int) => f"A$$i%0${length}d""""
  tb.eval(tb.parse(code)).asInstanceOf[Int => String]
}

val format = defFormat(length = 5)

format(21)

如果格式不好，将抛出

scala>   val code = raw"""(i: Int) => f"A$${i}%k0${10}d""""
code: String = (i: Int) => f"A${i}%k010d"

scala> tb.typecheck(tb.parse(code))
scala.tools.reflect.ToolBoxError: reflective typecheck has failed: illegal conversion character 'k'
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$typecheck$1.apply(ToolBoxFactory.scala:178)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$typecheck$1.apply(ToolBoxFactory.scala:170)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$11.apply(ToolBoxFactory.scala:148)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$11.apply(ToolBoxFactory.scala:148)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$9.apply(ToolBoxFactory.scala:138)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$9.apply(ToolBoxFactory.scala:138)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$withContext$1$1.apply(ToolBoxFactory.scala:139)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$withContext$1$1.apply(ToolBoxFactory.scala:139)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$7.apply(ToolBoxFactory.scala:137)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$7.apply(ToolBoxFactory.scala:137)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1.apply(ToolBoxFactory.scala:148)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1.apply(ToolBoxFactory.scala:121)
  at scala.reflect.internal.Trees$class.wrappingIntoTerm(Trees.scala:1716)
  at scala.reflect.internal.SymbolTable.wrappingIntoTerm(SymbolTable.scala:16)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal.withWrapping$1(ToolBoxFactory.scala:120)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal.transformDuringTyper(ToolBoxFactory.scala:121)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal.typecheck(ToolBoxFactory.scala:169)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$$anonfun$typecheck$2.apply(ToolBoxFactory.scala:375)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$$anonfun$typecheck$2.apply(ToolBoxFactory.scala:367)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$withCompilerApi$.liftedTree2$1(ToolBoxFactory.scala:355)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$withCompilerApi$.apply(ToolBoxFactory.scala:355)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl.typecheck(ToolBoxFactory.scala:367)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl.typecheck(ToolBoxFactory.scala:27)
  ... 32 elided

scala>   val code = raw"""(i: Int) => f"A$${i}%0${10}d""""
code: String = (i: Int) => f"A${i}%010d"

scala> tb.typecheck(tb.parse(code))
res19: tb.u.Tree =
((i: Int) => ({
  val arg$macro$9: Int = i;
  new scala.collection.immutable.StringOps("A%010d").format(arg$macro$9)
}: String))

---

您不能使用

f

执行此操作，因为它的全部目的是确保它可以检查格式字符串的类型错误，因此格式字符串必须是静态的

f

可以明确支持此场景，但它不支持

---

您可以将

格式化

设置为宏，但这似乎有些过分。更不用说它必须在一个单独的模块中定义，这在这种情况下看起来非常不方便。

我认为这可能会对您有所帮助：是的，但这里您使用的是格式化方法，而不是f字符串插值或您要求的“f插值器或其他”如果有帮助的话，我将添加工具箱暂存。因此，您构建函数来检查格式，然后构建代码来评估。这与使用完整编译器生成和加载类相反，在这种情况下，您只需发出要使用的函数？答案是：因为我是古董。

scala> import scala.tools.reflect._,scala.reflect.runtime._,universe._
import scala.tools.reflect._
import scala.reflect.runtime._
import universe._

scala> val tb = currentMirror.mkToolBox()
tb: scala.tools.reflect.ToolBox[reflect.runtime.universe.type] = scala.tools.reflect.ToolBoxFactory$ToolBoxImpl@2d10e0b1

scala> def f(n: Int)(i: Int): String = {
     |   val code = raw"""f"A$${$i}%0${n}d""""
     |   tb.eval(tb.parse(code)).asInstanceOf[String]
     | }
f: (n: Int)(i: Int)String

scala> val g = f(5) _
g: Int => String = <function1>

scala> g(21)
res9: String = A00021

scala> tb.typecheck(tb.parse(code))
scala.tools.reflect.ToolBoxError: reflective typecheck has failed: illegal conversion character 'k'
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$typecheck$1.apply(ToolBoxFactory.scala:178)

scala>   val code = raw"""(i: Int) => f"A$${i}%k0${10}d""""
code: String = (i: Int) => f"A${i}%k010d"

scala> tb.typecheck(tb.parse(code))
scala.tools.reflect.ToolBoxError: reflective typecheck has failed: illegal conversion character 'k'
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$typecheck$1.apply(ToolBoxFactory.scala:178)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$typecheck$1.apply(ToolBoxFactory.scala:170)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$11.apply(ToolBoxFactory.scala:148)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$11.apply(ToolBoxFactory.scala:148)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$9.apply(ToolBoxFactory.scala:138)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$9.apply(ToolBoxFactory.scala:138)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$withContext$1$1.apply(ToolBoxFactory.scala:139)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$withContext$1$1.apply(ToolBoxFactory.scala:139)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$7.apply(ToolBoxFactory.scala:137)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1$$anonfun$7.apply(ToolBoxFactory.scala:137)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1.apply(ToolBoxFactory.scala:148)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal$$anonfun$transformDuringTyper$1.apply(ToolBoxFactory.scala:121)
  at scala.reflect.internal.Trees$class.wrappingIntoTerm(Trees.scala:1716)
  at scala.reflect.internal.SymbolTable.wrappingIntoTerm(SymbolTable.scala:16)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal.withWrapping$1(ToolBoxFactory.scala:120)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal.transformDuringTyper(ToolBoxFactory.scala:121)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal.typecheck(ToolBoxFactory.scala:169)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$$anonfun$typecheck$2.apply(ToolBoxFactory.scala:375)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$$anonfun$typecheck$2.apply(ToolBoxFactory.scala:367)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$withCompilerApi$.liftedTree2$1(ToolBoxFactory.scala:355)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$withCompilerApi$.apply(ToolBoxFactory.scala:355)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl.typecheck(ToolBoxFactory.scala:367)
  at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl.typecheck(ToolBoxFactory.scala:27)
  ... 32 elided

scala>   val code = raw"""(i: Int) => f"A$${i}%0${10}d""""
code: String = (i: Int) => f"A${i}%010d"

scala> tb.typecheck(tb.parse(code))
res19: tb.u.Tree =
((i: Int) => ({
  val arg$macro$9: Int = i;
  new scala.collection.immutable.StringOps("A%010d").format(arg$macro$9)
}: String))