Question

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C#: Structs versus classes

I am creating a library, which is relatively small to require a database, containing tags of MP3 files.

I know that it would be better to stick with structures if I have fixed size data like integers, doubles etc… However in my case, I have strings and lists that contains strings and even other structures… If I will go with structures, it will look like this:

Public Structure STitle
    Dim Title As String
    Dim Path As String
End Structure

Public Structure SAlbum
    Dim Album As String
    Dim Songs As List(Of STitle)
End Structure

Public Structure SArtist
    Dim Artist As String
    Dim Albums As List(Of SAlbum)
End Structure

Then, I will have something like this:

Public SongLibrary As New List(Of SArtist)

The strings and lists are confusing me, especially speed-wise. Since I will be searching through lots of song, I want to make sure that I am using the fastest one.

I am also confused about boxing and unboxing. I assume that the list of string contains only the pointers to “the string” and same for the structures(trying to think low level). However, I don’t know whether boxing-unboxing, which slows down the searching(a reason to not to use arraylists), takes place or not since the sizes are impossible to determine(or is it?)

So which one to pick? Class, or structure? or is there something else suiting better?

Answer 1

I know that it would be better to stick with structures if I have fixed size data like integers, doubles etc

How do you “know” that? In my experience, it’s very rarely a good idea to create a custom value type. It does happen – there are plenty in my Noda Time project, for example – but usually I would be wary. I’d also be very wary before exposing mutable structures.

I am also confused about boxing and unboxing. I assume that the list of string contains only the pointers to “the string” and same for the structures(trying to think low level).

For structures, there isn’t a pointer (reference). A List(Of Integer) is implemented with an Integer() for example. The array contains the values directly. With generic collections, no boxing is required.

See the class design guidelines for more information, but basically I’d default to using classes unless I had a really compelling reason to create a structure.