Groovy - How to overload '+=' operator in a Map with compile static? - groovy

Question

In Groovy, I can overload operator '+' plus as follow:
class MutableInt {
int val
MutableInt(int val) { this.val = val }
MutableInt plus(int val) {
return new MutableInt(this.val += val)
}
}
The above class works fine for the following test cases:
def m1 = new MutableInt(1);
assert (m1 + 1).val == 2;
However, if I need to use it together with Map like this and compile it with static
#groovy.transform.CompileStatic
void compileItWithStatic() {
Map<Long, MutableInt> mutMap = [:].withDefault{ new MutableInt(0) }
assert (mutMap[1L] += 20).val == 20;
}
compileItWithStatic()
I got the following error:
*Script1.groovy: 17: [Static type checking] -
Cannot call <K,V> java.util.Map <java.lang.Long, MutableInt>#putAt(java.lang.Long, MutableInt) with arguments [long, int]*
How can I override the '+=' operator and compile it with static without error?
EDIT:
If I am doing like this without compile static it works fine:
def m1 = new MutableInt(1);
assert (m1 += 1).val == 2 // <----- caution: '+=' not '+' as in previous case
However, if it was inside the method like this:
#groovy.transform.CompileStatic
void compileItWithStatic_2() {
def m1 = new MutableInt(1);
assert (m1 += 1).val == 2
}
The error will be:
Script1.groovy: -1: Access to java.lang.Object#val is forbidden # line -1, column -1.
1 error
P.S. It won't work with static compilation not with dynamic compilation.

Answer 1

The assignment part is throwing the error. A simple + works:
class MutableInt {
int val
MutableInt(int val) { this.val = val }
MutableInt plus(int val) {
return new MutableInt(this.val += val)
}
}
def m1 = new MutableInt(1);
assert (m1 + 1).val == 2;
#groovy.transform.CompileStatic
def compileItWithStatic() {
Map<Long, MutableInt> mutMap = [:].withDefault{ new MutableInt(0) }
mutMap[1L] + 20
mutMap
}
assert compileItWithStatic()[1L].val == 20
Groovy is parsing mutMap[1L] += 20 as mutMap.putAt(1L, 20). This looks like a bug to me. This works: mutMap[1L] = mutMap[1L] + 20, albeit more verbose.
Edit: the second error seems related to the result of the expression (m1 + 1) being parsed as Object. This should work:
#groovy.transform.CompileStatic
void compileItWithStatic_2() {
def m1 = new MutableInt(1) + 1;
assert m1.val == 2
}