Question

This question derives from the reason I asked my last question on foreach loops. I have a large string array (say in the thousands), and I want to iterate through the array and also be able to break out based on a certain condition, and I need optimal performance.

Some example code:

for(int i = 0; i < array.length && flag == true; i++){
    //Processing and set flag
}

//..or

foreach(string item in array){
    //processing...set flag
    if(!flag)
        break;
}

Which way would be less expensive?

Answer 1

You can always benchmark them. Use a Stopwatch and iterate over, say, ten million iterations to see which goes faster.

What I think you’ll find, though, is that the two are nearly identical since the JIT compiler optimizes foreach on an array to basically a for.

flevine100 is actually right that in general a for is slightly more efficient than a foreach for types whose GetEnumerator methods create a new object implementing IEnumerator or IEnumerator<T> (due to the memory allocation and method call overhead); this is less the case for most of the collections in System.Collections.Generic, however, due to their explicit IEnumerable implementation using value type enumerators (not to mention that the foreach construct does not actually require an IEnumerable implementation in the first place).

It’s even less the case for arrays specifically because they are fixed-size and therefore trivial to optimize by the JIT compiler.