"Dynamic" method invocation with new Scala reflection API

Question

In olden times, when Invocation, an experimental utility, was a part of standard library, one could invoke methods "dynamically" as shown below:

"Hello!" o 'substring(0, 4)  // to get Any back
"Hello!" oo 'substring(0, 4) // for an automatic unsafe cast to expected type

How to do this with the new Scala reflection API?

Why do you want to call methods at runtime when you already know their names/identifiers/parameters? Is there something you can't achieve at compile time? — kiritsuku, Jun 16 '12 at 19:52
@Antoras, only curious. Not really using this stuff in production. — missingfaktor, Jun 17 '12 at 04:44

score 25 · Accepted Answer · edited May 23 '17 at 10:31

Welcome to Scala version 2.10.0-20120617-072418-9a28ee1ffc (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_33).
Type in expressions to have them evaluated.
Type :help for more information.

scala> class Foo { def bar(x: Int) = x }
defined class Foo

scala> val foo = new Foo
foo @ 5935b50c: Foo = Foo@5935b50c

scala> runtimeMirror(getClass.getClassLoader).reflect(foo)
res0 @ 65c24701: reflect.runtime.universe.InstanceMirror = scala.reflect.runtime.JavaMirrors$JavaMirror$JavaInstanceMirror@65c24701

scala> res0.symbol.typeSignature.member(newTermName("bar"))
res1 @ 69624a1c: reflect.runtime.universe.Symbol = method bar

scala> res0.reflectMethod(res1.asMethodSymbol)(42)
res2 @ 4ac1d188: Any = 42

Some background information about how the API is designed can be found here: Get companion object instance with new Scala reflection API.

"Dynamic" method invocation with new Scala reflection API

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