tracker issue : CF-4010308

I believe there is a serious bug with the for-in construct when used in a particular fashion. In particular, if the "in" expression is a function call, it appears that the function is invoked multiple times (to be precise, it always appears to be 5 times).

Clearly there are many situations where this could have serious consequences, not least if the function does any serious work or has side effects.

Key points:

Tested on Coldfusion 10 update 16
Using a for-in construct where the "in" expression invokes a function results in that function being invoked multiple times.
It doesn't seem to matter what the function returns (e.g. struct, array, potentially other iterables)

Workaround:

Assign the result of the function call to a local variable outside the for-in construct

Severity:

This a serious issue as,

It is easy to cause using a common idiom
It is completed unexpected
The fact that it is happening is essentially invisible to the developer
The results are potentially very serious

Speculation:

I speculate that the code is pre-processed into a construct that does (in clause).size() (in clause).iterator(), etc

Test Case:

See below for some code which tests this:

component displayname="ForInTest" {

  ForInTest function init() {
    variables.count = 0;
    return this;
  }

  void function test1() {
    variables.count = 0;

    for( var item in getArray() ) {
      // do something interesting
    }

    if( variables.count==1 ) {
      writeoutput( "getArray() was called once." );
    }
    else {
      writeoutput( "getArray() was called multiple times! (" & variables.count & ")" );
    }
  }

  void function test2() {
    variables.count = 0;

    var items = getArray();
    for( var item in items ) {
      // do something interesting
    }

    if( variables.count==1 ) {
      writeoutput( "getArray() was called once." );
    }
    else {
      writeoutput( "getArray() was called multiple times! (" & variables.count & ")" );
    }
  }

  private array function getArray() {
    variables.count++;
    var data = [1,2,3];
    return data;
  }
}

var test = new ForInTest();
test.test1();
test.test2();

Output:
getArray() was called multiple times! (5)
getArray() was called once.

----------------------------- Additional Watson Details -----------------------------

Watson Bug ID:	4010308

External Customer Info:
External Company:  
External Customer Name: Lewis
External Customer Email:  
External Test Config: My Hardware and Environment details:

Attachments:

Comments: