Constructor return pointer to existing instance

Question

I'm wondering how to create a default class constructor. I do not want to waste resources, so I just want the constructor to return a pointer to an already existing instance of the class.

This is what I thought of. Obviously, it doesn't work, but I want to follow this code's logic.

public Sprite()
{
  return Default.MissingSprite;
}

public Sprite(Texture2D texture, SpriteDrawMode drawMode)
{
  if (drawMode != SpriteDrawMode.Sliced) throw new ArgumentException("...");
  this.texture = texture;
  this.drawMode = drawMode;
  this.sliceFraction = Default.SpriteSliceFraction;
}

public Sprite(Texture2D texture, SpriteDrawMode drawMode, float sliceFraction)
{
  this.texture = texture;
  this.drawMode = drawMode;
  this.sliceFraction = sliceFraction;
}

I know constructors are void, so I can't return in them.

I do NOT want to just assign the values of the default instance, as that would waste memory, since it would just create a duplicate of the default instance

//This is what I do NOT want
public Sprite()
{
  this.texture = Default.MissingSprite.texture;
  this.drawMode = Default.MissingSprite.drawMode;
  this.sliceFraction = Default.MissingSprite.sliceFraction;
}

Is what I'm trying to achieve possible? Are there any design problems with my thought process?

Answer 1

You want to do two operations, one is to create an instance and the other is to return some value Default.MissingSprite . This is not possible in C#.

---

What you should do is create a property which addresses the state and holds that value such as

public SpriteState State { get; set;}

Then upon creation ( like you have in your example )

public Sprite()
{
   State = Default.MissingSprite;
} 

Then set other State s in the other constructors as appropriate.

Finally it is up to the user to check the State property before usage.

var mySprite = new Sprite();

// Some code which could change the State...

switch (mySprite.State)
{
   case Default.MissingSprite:
      ...
   break;

   case Default.OkSprite:
      ...
   break;
  ...