Groovy: Timeduration-Subtraction evaluated from string - string

Question

My script reads a string from a file and evaluates it to work as TimeDuration within TimeCategory. If the string starts with a "-" it throws an Exception.
My reduced script:
import groovy.time.TimeCategory;
String string = "-1.day"
Date now = new Date()
use(TimeCategory)
{
def x = new Date() + evaluate(string)
println x
}
Throws:
groovy.lang.MissingMethodException: No signature of method: groovy.time.Duration.negative() is applicable for argument types: () values: []
Possible solutions: notify()
At the moment my solution would be this:
import groovy.time.TimeCategory;
String string = "-1.day"
Date now = new Date()
use(TimeCategory)
{
def x
if(string.startsWith("-"))
{
string = string.substring(1)
x = now - evaluate(string)
}
else
{
x = now + evaluate(string)
}
println x
}
It could although do the following. But... i dont like it. I'm not sure about the consequence (will it work with different time units? "-1.day+2.hours-3.minutes"):
String prestring = "-1.day"
String string = "0.day$prestring"
Any suggestions?

Answer 1

The problem is the order the operations are evaluated in:
-1.day is equivalent to -(1.day), or (1.day).negative()
To solve this, you can apply parentheses to evaluate the minus operator first:
(-1).day
Another solution is to add a negative() method to the Duration class.
Duration.metaClass.negative = { ->
new Duration(-delegate.days,
-delegate.hours,
-delegate.minutes,
-delegate.seconds,
-delegate.millis)
}