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Iterators in ColdFusion
Last update:
May 18, 2026
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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