[ Groovy 常見問題 ] how to accept multiple parameters from returning function in groovy

Source From Here 
Question 
I want to return multiple values from a function written in groovy and receive them , but i am getting an error: 
 

The code: 

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1. int a=10  
2. int b=0  
3. println "a is ${a} , b is ${b}"  
4. [a,b]=f1(a)  
5. println "a is NOW ${a} , b is NOW ${b}"  
6.   
7. def f1(int x) {     
8.   return [a*10,a*20]  
9. }  

How-To 
You almost have it. [ a, b ] creates a list, and ( a, b ) unwraps one, so you want (a,b)=f1(a) instead of [a,b]=f1(a). 

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1. int a=10  
2. int b=0  
3. println "a is ${a} , b is ${b}"  
4. (a,b)=f1(a)  
5. println "a is NOW ${a} , b is NOW ${b}"  
6.   
7. def f1(int x) {  
8.     return [x*10,x*20]  
9. }  

By the way, if you want to retrieve key/value of Map as tuple, you can refer to below code: 

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1. import java.util.Map.Entry  
2.   
3. def m = ['a':1, 'b':2]  
4.   
5. def e = m.entrySet()  
6.   
7. class MapItems implements Iterable{  
8.     Set mapSet;  
9.       
10.     public MapItems(Set mset)  
11.     {  
12.         this.mapSet = mset  
13.     }  
14.       
15.     class _Iter implements Iterator{  
16.         Iterator iter  
17.           
18.         public _Iter(Iterator i){iter=i}  
19.   
20.         @Override  
21.         public boolean hasNext() {  
22.             iter.hasNext();  
23.         }  
24.   
25.         @Override  
26.         public List next() {  
27.             Entry e = iter.next()  
28.             return [e.key, e.value]  
29.         }  
30.   
31.         @Override  
32.         public void remove() {  
33.             throw new java.lang.UnsupportedOperationException()           
34.         }         
35.     }  
36.   
37.     @Override  
38.     public Iterator iterator() {  
39.         new _Iter(mapSet.iterator())  
40.     }  
41. }  
42.   
43. Map.metaClass.items = {return new MapItems(delegate.entrySet())}  
44.   
45. Iterator itemIter = m.items().iterator()  
46. while(itemIter.hasNext())  
47. {  
48.     // Retrieve key/value as tuple  
49.     (k,v) = itemIter.next()  
50.     printf("$k=$v\n")  
51. }  

Supplement 
* [ Groovy Doc ] ExpandoMetaClass - Domain-Specific Language