Question

I have a list: List<MyClass> MyList = new List<MyClass>();.

MyClass has methods SetBool and IsTrue. I have to set every object of this list to false (obj.SetBool(false)).

There are 2 possible ways:

First:

foreach (MyClass obj in MyList)
{
    obj.SetBool(false)
}

Second:

List<MyClass> MyList2 = MyList.Where(c => c.IsTrue()).ToList();

foreach (MyClass obj in MyList2)
{
    obj.SetBool(false)
}

If I use first one it may be slow because it changes every element. The second way can be slow too, because it has to find objects first.

So my question is:
Which one will be faster (I may have very large number of elements in list) and why?

Answer 1

Fastest would be the combination:

foreach (MyClass obj in MyList)
{
    if (obj.IsTrue())
        obj.SetBool(false)
}

But the difference with your first version will only be meaningful when SetBool() does some extensive validations or computation, and is much more expensive than Istrue().