Iterators in ColdFusion

In ColdFusion, an iterator is an object, which defines a sequence and a return value upon its termination. The iterator protocol defines a standard way to produce a sequence of values (either finite or infinite), and potentially a return value when all values have been generated.

ColdFusion Components can be made iterable and UDF's are used as iterators.

How to make a cfc iterable ?               

If the CFC implements __iter__ function with no arguments it will be called to get the iterator instance. The iterable function can return array, String, query, function (like below) or a cfc which has a function named __next()__.

CFC as an iterator

// Iterator.cfc 
component { 
    public any function __next__(previous, count){ // Follows Iteration Protocol as UDF 
    return {value: count+1, done: count > 11}; 
} 
}
# cfcAsIterator.cfc 
component { 
   public any function __iter__() { 
      return new Iterator(); 
   } 
}
// stringAsIterator.cfc 
component{ 
    public any function __iter__() { 
      
    str1="ColdFusion 2021"; 
    str2="Project Stratus"; 
      return [...str1,...str2]; 
   } 
}

UDF as iterator

// udfAsIterator.cfc 
//Example using UDF as Iterator and CFC is the Iterable 
component { 
   public any function __iter__() { 
      var startFrom = 100; 
      return function(previous, index){//Iterator UDF 
         return {"value": startFrom + index, "done": index > 9}; 
      } 
   } 
}
// udfAsIterator.cfm 
<cfscript> 
/* 
Plain UDF/Closure/Lambda as Iterator 
Invoking iterators using forin loop 
 
*/ 
 iterator = (previous, count) =>{ 
   
  return {"value": count + 2, "done": count > 9}; 
 }; 
 
 writeoutput("----------- UDF/Closure/Lambda as Iterator -------------<hr>") 
 for(i in iterator) { 
  writeoutput(i & " " & "<br>"); 
 } 
  
 udfIteratorOBj = new udfAsIterator(); 
 stringIteratorObj= new stringAsIterator(); 
 cfcIteratorObj = new cfcAsIterator(); 
  
   
  writeoutput("<br>----------- UDF as Iterator -------------<hr>") 
  for(i in udfIteratorOBj) { 
   writeoutput(SerializeJson(i) & "<br>"); 
 } 
 writeoutput("<br>----------- String as Iterator -------------<hr>") 
  for(i in stringIteratorObj) { 
   writeoutput(SerializeJson(i) & "<br>"); 
 } 
  
 writeoutput("<br>----------- CFC as Iterator -------------<hr>") 
 for(i in cfcIteratorObj ) { 
   writeoutput(SerializeJson(i) & "<br>"); 
 } 
</cfscript>

Output

----------- UDF/Closure/Lambda as Iterator -------------
3 4 5 6 7 8 9 10 11 12

----------- UDF as Iterator -------------
101.0102.0103.0104.0105.0106.0107.0108.0109.0110.0

----------- String as Iterator -------------
"C""o""l""d""F""u""s""i""o""n"" ""2""0""2""1""P""r""o""j""e""c""t"" ""S""t""r""a""t""u""s"

----------- CFC as Iterator -------------
2.03.04.05.06.07.08.09.010.011.012.013.0

Array as iterator

// arrayAsIteratorwithSpread.cfc 
component{ 
 public any function __iter__() { 
  
 arr1=[1,2,3] 
 arr2=[4,5,6] 
      return [...arr1,...arr2]; 
   } 
    
   function demofunc(){ 
    
 return "demostring!" 
    
   } 
}
// arrayAsIterator.cfm 
<cfscript> 
 arrayIteratorObj1= new arrayAsIteratorwithSpread(); 
 
writeoutput("<br>----------- Array as Iterator 1-------------<hr>") 
 for(i in arrayIteratorObj1 ) { 
   writeoutput(i & "<br>"); 
 } 
 
</cfscript>

Output

123456

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