我应该在哪里存储不同类型的值？

Question

After Python and JavaScript I started using C# and can't understand some basic concepts.

In Python and JavaScript I used to store everything in a heap without thinking about the type of object. But in C# I can't create Dictionary or List with different type of object.

I want to store some mouse and keyboard events. For that, I use instances of class, like this:

class UserActionEvent
{
    public MacroEventType Type;
    public int[] MouseCoordinate = new int[2];
    public string MouseKey;
    public string KeyBoardKey;
    public int TimeSinceLastEvent;
}

And all instances is saved in Queue . But I worry whether it is normal to store several thousand objects like this? Maybe there is a more universal way to store data of different types?

Answer 1

Storage in C# is not much different from Python in JavaScript in that it uses a garbage collected heap (of course every runtime has its own way of implementing the GC). So for "normal" classes you can just go ahead and treat them as you would in JS.

C#, however, also has the concept of value types , which are typically allocated on the stack. The stack has a much more limited space than the heap, so this is where you need to be a bit more careful, but it is unlikely that you accidentally allocate a large amount of stack space, since collection types are all reference types (with the exception of the more exotic stackalloc arrays that you should stay away from unless you are sure what you are doing). When passing value types between methods, they are copied, but it is also possible to pass them by reference (for example by casting to object ). This will wrap the value type in a reference type, a process called boxing (the opposite process is called unboxing ).

To create a value type, use struct instead of class . In your example above, using a value type for the mouse coordinate, eg

struct Point {
    public int X, Y;
}

instead of an int array would likely save memory (and GC CPU time) since in your example you would have to allocate a reference object (the array) to hold only eight bytes (the two ints). But this only matters in more exotic cases, maybe in the render loop of a game engine, or if you have huge data sets. For most type of programs this is likely to be premature optimization (though one could argue creating the struct would make the code more readable, which would likely then be the main benefit).

Some useful reads:

• https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/value-types
• https://medium.com/fhinkel/confused-about-stack-and-heap-2cf3e6adb771
• https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/stackalloc

Answer 2

If you want to store different type of objects on c# I recommend the use of ArrayList With ArrayList you can store any type of object since it is a dynamic collection of objects.

  ArrayList myAL = new ArrayList();
  myAL.Add("Hello");
  myAL.Add("World");
  myAL.Add("!");

You will need a using System.Collections; To be abel to use this collection