const mixinafBeanUtils::NotFoundErr

Implement on user defined Errs to list available values in the stack trace. This gives the user helpful context when a value could not be found. Typical usage would be:

const class MyNotFoundErr : Err, NotFoundErr {
   override const Str?[] availableValues
   
   new make(Str msg, Obj?[] availableValues, Err? cause := null) : super(msg, cause) {
      this.availableValues = availableValues.map { it?.toStr }.sort
   }
   
   override Str toStr() {
      NotFoundErr.super.toStr
   }
}

Which when thrown with:

throw MyNotFoundErr("Could not find a sausage.", ["steak", "hot dog", "burger"])

Gives a helpful stack trace of:

MyNotFoundErr: Could not find a sausage.

Available values:
  burger
  hot dog
  steak

Stack Trace:
  afTest::Wotever.main (Wotever.fan:69)
  java.lang.reflect.Method.invoke (Method.java:597)
  fan.sys.Method.invoke (Method.java:559)
  fan.sys.Method$MethodFunc.callOn (Method.java:230)
  fanx.tools.Fan.callMain (Fan.java:175)
  fanx.tools.Fan.executeType (Fan.java:140)
  ...

Note that BedSheet gives special treatment to NotFoundErrs on its standard Err 500 page and lists the available values in its own section.