How is myArray.size() implemented in Salesforce Apex? Does the method retrieve a value stored on the List.class object, or calculated at time of call?

Question

Often when I'm writing a loop in Apex, i wonder if it's inefficient to call myArray.size() inside of a loop. My question is really: should I use myArray.size() inside the loop, or store myArray.Size() in an Integer variable before starting the loop and reuse that instead (assuming the size of myArray remains constant).

Under the hood, the method either counts each element of an array by iterating through it and incrementing a size variable which it then returns, or the List/Set/Map etc class stores the size variable inside itself and updates the value any time the array is changed. Different languages handle this in different ways, so how does Apex work?

I went searching but couldn't find an answer. The answer could change the way I code, since calling myArray.size() could exponentially increase the number of operations performed when called inside a loop.

I tried running a benchmark of the two scenarios as laid out below and found that myList.size() does take longer, but didn't really answer my question. Especially since the code was too simple to really make much of a difference.

In both samples, the list has ten thousand elements, and I only started timing once the list is fully created. The loop itself doesn't do anything interesting. It just counts up. That was the least resource heavy thing I could think of.

Sample 1 - store size of list in an integer before entering loop:

List<Account> myArray = [SELECT Id FROM Account LIMIT 10000];

Long startTime = System.now().getTime();
Integer size = myArray.size();

Integer count = 0;
for (Integer i = 0; i < 100000; i++) {
    if (count < size) {
        count++;
    }
}

Long finishTime = System.now().getTime();

Long benchmark = finishTime - startTime;
System.debug('benchmark: ' + benchmark);

Results after running 5 times: 497, 474, 561, 445, 474

Sample 2 - use myArray.size() inside loop:

List<Account> myArray = [SELECT Id FROM Account LIMIT 10000];


Long startTime = System.now().getTime();

Integer count = 0;
for (Integer i = 0; i < 100000; i++) {
    if (count < myArray.size()) {
        count++;
    }
}

Long finishTime = System.now().getTime();

Long benchmark = finishTime - startTime;
System.debug('benchmark: ' + benchmark);

Results after running 5 times: 582, 590, 667, 742, 730

Sample 3 - just for good measure (control), here's the loop without the if condition:

Long startTime = System.now().getTime();

Long count = 0;
for (Integer i = 0; i < 100000; i++) {
    count++;
}

Long finishTime = System.now().getTime();

Long benchmark = finishTime - startTime;
System.debug('benchmark: ' + benchmark);

Results after running 5 times: 349, 348, 486, 475, 531