Question

I have sample code as below

import org.codehaus.groovy.control.CompilerConfiguration

abstract class MyClass extends Script {

    void testMethod(Integer x) {
        println "x = $x"
    }
}

public static void main(String[] args) {
    compilerConfiguration = new CompilerConfiguration();
    compilerConfiguration.setScriptBaseClass("MyClass");
    GroovyShell shell = new GroovyShell(new Binding(), compilerConfiguration);
    shell.evaluate("testMethod 1")
}

When I run this class it prints x = 1
now if I change the "testMethod 1" to "testMethod -1" it fails with

Caught: groovy.lang.MissingPropertyException: No such property: testMethod for class: Script1
groovy.lang.MissingPropertyException: No such property: testMethod for class: Script1
    at Script1.run(Script1.groovy:1)
    at Test.run(Test.groovy:15)

Now I change "testMethod -1" to "testMethod (-1)". It again works and printed x = -1

What I need to understand is why Groovy is asking for the parentheses for negative numbers.

Answer 1

Because without parentheses, it is assuming you are trying to subtract 1 from a property called testMethod (ie: testMethod - 1)

You need the parentheses to inform the parser that this is a method call rather than a subtraction operation

---

Edit

I came up with a horrible way to get this to work:

import java.lang.reflect.Method
import org.codehaus.groovy.control.CompilerConfiguration

abstract class MyClass extends Script {
  private methods = [:]
  
  class MinusableMethod {
    Script declarer
    Method method
    MinusableMethod( Script d, Method m ) {
      this.declarer = d
      this.method = m
    }
    def minus( amount ) {
      method.invoke( declarer, -amount )
    }
  }

  public MyClass() {
    super()
    methods = MyClass.getDeclaredMethods().grep {
      it.name != 'propertyMissing' && !it.synthetic
    }.collectEntries {
      [ (it.name): new MinusableMethod( this, it ) ]
    } 
  }

  def propertyMissing( String name ) {
    methods[ name ]
  }

  void testMethod(Integer x) {
      println "x = $x"
  }
}

static main( args ) {
  def compilerConfiguration = new CompilerConfiguration();
  compilerConfiguration.setScriptBaseClass( 'MyClass' );
  GroovyShell shell = new GroovyShell(new Binding(), compilerConfiguration);
  shell.evaluate("testMethod - 1")
}

But this will probably break under other conditions

In the long run, getting people to write valid scripts is probably the better route to take…