C# List.ToArray performance is bad?

Question

I\'m using .Net 3.5 (C#) and I\'ve heard the performance of C# List.ToArray is \"bad\", since it memory copies for all elements to form a new array. Is

Answer 1

Reasons to call ToArray()

• If the returned value is not meant to be modified, returning it as an array makes that fact a bit clearer.
• If the caller is expected to perform many non-sequential accesses to the data, there can be a performance benefit to an array over a List<>.
• If you know you will need to pass the returned value to a third-party function that expects an array.
• Compatibility with calling functions that need to work with .NET version 1 or 1.1. These versions don't have the List<> type (or any generic types, for that matter).

Reasons not to call ToArray()

• If the caller ever does need to add or remove elements, a List<> is absolutely required.
• The performance benefits are not necessarily guaranteed, especially if the caller is accessing the data in a sequential fashion. There is also the additional step of converting from List<> to array, which takes processing time.
• The caller can always convert the list to an array themselves.

taken from here