从字符串生成一个类并在 Scala 2.10 中实例化它
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Generating a class from string and instantiating it in Scala 2.10
提问by Nikita Volkov
In Scala 2.10 how do I generate a class from string (probably, using the Toolbox api) later to be instantiated with Scala's reflection?
在 Scala 2.10 中，如何从字符串（可能使用 Toolbox api）生成一个类，以便稍后使用 Scala 的反射进行实例化？
回答by Eugene Burmako
W.r.t compilation toolboxes can only run expressions = return values, but not resulting classes or files/byte arrays with compilation results.
Wrt 编译工具箱只能运行表达式 = 返回值，但不能运行带有编译结果的类或文件/字节数组。
However it's still possible to achieve what you want, since in Scala it's so easy to go from type level to value level using implicit values:
然而，仍然有可能实现您想要的，因为在 Scala 中使用隐式值很容易从类型级别转到值级别：
Edit. In 2.10.0-RC1 some methods of ToolBoxhave been renamed. parseExpris now just parse, and runExpris now called eval.
编辑。在 2.10.0-RC1 中，某些方法ToolBox已重命名。parseExpr现在只是parse，runExpr现在被称为eval。
scala> import scala.reflect.runtime._ // requires scala-reflect.jar
// in REPL it's implicitly added
// to the classpath
// but in your programs
// you need to do this on your own
import scala.reflect.runtime
scala> val cm = universe.runtimeMirror(getClass.getClassLoader)
cm @ 41d0fe80: reflect.runtime.universe.Mirror = JavaMirror with scala.tools.nsc.interpreter.IMain$TranslatingClassLoader...
scala> import scala.tools.reflect.ToolBox // requires scala-compiler.jar
// in REPL it's implicitly added
// to the classpath
// but in your programs
// you need to do this on your own
import scala.tools.reflect.ToolBox
scala> val tb = cm.mkToolBox()
tb: scala.tools.reflect.ToolBox[reflect.runtime.universe.type] = scala.tools.reflect.ToolBoxFactory$ToolBoxImpl@3a962da5
scala> tb.runExpr(tb.parseExpr("class C; scala.reflect.classTag[C].runtimeClass"))
res2: Any = class __wrapper$f9d572ca0d884bca9333e251c64e980d$C
Update #1. If you don't need a java.lang.Class and just need to instantiate the compiled class, you can write new Cdirectly in the string submitted to runExpr.
更新#1。如果不需要java.lang.Class，只需要实例化编译后的类，new C直接在提交到的字符串中写即可runExpr。
Update #2. It is also possible to have runExpruse custom mapping from variable names to runtime values. For example:
更新#2。也可以runExpr使用从变量名称到运行时值的自定义映射。例如：
scala> val build = scala.reflect.runtime.universe.build
build: reflect.runtime.universe.BuildApi = scala.reflect.internal.BuildUtils$BuildImpl@50d5afff
scala> val x = build.setTypeSignature(build.newFreeTerm("x", 2), typeOf[Int])
x: reflect.runtime.universe.FreeTermSymbol = free term x
scala> tb.runExpr(Apply(Select(Ident(x), newTermName("$plus")), List(Literal(Constant(2)))))
res0: Any = 4
In this example I create a free term that has a value of 2 (the value doesn't have to be a primitive - it can be your custom object) and bind an identifier to it. This value is then used as-is in the code that is compiled and run by a toolbox.
在本例中，我创建了一个值为 2 的自由项（该值不必是原始值 - 它可以是您的自定义对象）并将标识符绑定到它。然后在由工具箱编译和运行的代码中按原样使用该值。
The example uses manual AST assembly, but it's possible to write a function that parses a string, finds out unbound identifiers, looks up values for them in some mapping and then creates corresponding free terms. There's no such function in Scala 2.10.0 though.
该示例使用手动 AST 汇编，但可以编写一个函数来解析字符串，找出未绑定的标识符，在某些映射中查找它们的值，然后创建相应的自由项。但是 Scala 2.10.0 中没有这样的功能。
