How and when to abandon the use of arrays in C#?

Question

I've always been told that adding an element to an array happens like this:

An empty copy of the array+1element is created and then the data from the original array is copied into it then the new data for the new element is then loaded

If this is true, then using an array within a scenario that requires a lot of element activity is contra-indicated due to memory and CPU utilization, correct?

If that is the case, shouldn't you try to avoid using an array as much as possible when you will be adding a lot of elements? Should you use iStringMap instead? If so, what happens if you need more than two dimensions AND need to add a lot of element additions. Do you just take the performance hit or is there something else that should be used?

Answer 1

Look at the generic List<T> as a replacement for arrays. They support most of the same things arrays do, including allocating an initial storage size if you want.

Answer 2

This really depends on what you mean by "add."

If you mean:

T[] array; int i; T value; ... if (i >= 0 && i <= array.Length)     array[i] = value; 

Then, no, this does not create a new array, and is in-fact the fastest way to alter any kind of IList in .NET.

If, however, you're using something like ArrayList, List, Collection, etc. then calling the "Add" method may create a new array -- but they are smart about it, they don't just resize by 1 element, they grow geometrically, so if you're adding lots of values only every once in a while will it have to allocate a new array. Even then, you can use the "Capacity" property to force it to grow before hand, if you know how many elements you're adding (list.Capacity += numberOfAddedElements)