使用 out/ref 与返回有什么好处

我正在使用XNA框架制作游戏，所以我使用了很多对向量进行操作的函数。(特别是矢量2(64位结构((。困扰我的是大多数方法都是使用 ref 和 out 参数定义的。下面是一个示例：

void Min(ref Vector2 value1, ref Vector2 value2, out Vector2 result)

这看起来也有点奇怪。还有一种Min更明显

public static Vector2 Min(Vector2 value1, Vector2 value2);

基本上，几乎所有函数都有 ref s 和 out s 的重载。

这种设计有什么好处？XNA 针对性能进行了优化，这可能是一个结果吗？比如说，四元数需要 128b，其中通过 ref 更少。

编辑：

下面是一个测试代码：

public class Game1 : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;
    private Vector2 vec1 = new Vector2(1, 2);
    private Vector2 vec2 = new Vector2(2, 3);
    private Vector2 min;
    private string timeRefOut1;
    private string timeRefOut2;
    private SpriteFont font;
    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
        refOut1();
        refOut2();
    }
    private Vector2 refOut1()
    {
        Vector2 min = Vector2.Min(vec1, vec2);
        return min;
    }
    private Vector2 refOut2()
    {
        Vector2.Min(ref vec1, ref vec2, out min);
        return min;
    }
    protected override void Initialize()
    {
        const int len = 100000000;
        Stopwatch stopWatch = new Stopwatch();
        stopWatch.Start();
        for (int i = 0; i < len; i++)
        {
            refOut1();
        }
        stopWatch.Stop();
        timeRefOut1 = stopWatch.ElapsedMilliseconds.ToString();
        stopWatch.Reset();
        stopWatch.Start();
        for (int i = 0; i < len; i++)
        {
            refOut2();
        }
        stopWatch.Stop();
        timeRefOut2 = stopWatch.ElapsedMilliseconds.ToString();
        base.Initialize();
    }
    protected override void LoadContent()
    {
        spriteBatch = new SpriteBatch(GraphicsDevice);
        font = Content.Load<SpriteFont>("SpriteFont1");
    }
    protected override void Update(GameTime gameTime)
    {
        if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
            this.Exit();
        base.Update(gameTime);
    }
    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);
        spriteBatch.Begin();
        spriteBatch.DrawString(font, timeRefOut1, new Vector2(200, 200), Color.White);
        spriteBatch.DrawString(font, timeRefOut2, new Vector2(200, 300), Color.White);
        spriteBatch.End();
        // TODO: Add your drawing code here
        base.Draw(gameTime);
    }
}

结果：

• 编号1 2200
• 编号2 1400

赢 7 64 位，.Net 4。XNA 4.0

还有 IL 代码

.method public hidebysig static void  Min(valuetype Microsoft.Xna.Framework.Vector2& value1,
                                          valuetype Microsoft.Xna.Framework.Vector2& value2,
                                          [out] valuetype Microsoft.Xna.Framework.Vector2& result) cil managed
{
  // Code size       69 (0x45)
  .maxstack  3
  IL_0000:  ldarg.2
  IL_0001:  ldarg.0
  IL_0002:  ldfld      float32 Microsoft.Xna.Framework.Vector2::X
  IL_0007:  ldarg.1
  IL_0008:  ldfld      float32 Microsoft.Xna.Framework.Vector2::X
  IL_000d:  blt.s      IL_0017
  IL_000f:  ldarg.1
  IL_0010:  ldfld      float32 Microsoft.Xna.Framework.Vector2::X
  IL_0015:  br.s       IL_001d
  IL_0017:  ldarg.0
  IL_0018:  ldfld      float32 Microsoft.Xna.Framework.Vector2::X
  IL_001d:  stfld      float32 Microsoft.Xna.Framework.Vector2::X
  IL_0022:  ldarg.2
  IL_0023:  ldarg.0
  IL_0024:  ldfld      float32 Microsoft.Xna.Framework.Vector2::Y
  IL_0029:  ldarg.1
  IL_002a:  ldfld      float32 Microsoft.Xna.Framework.Vector2::Y
  IL_002f:  blt.s      IL_0039
  IL_0031:  ldarg.1
  IL_0032:  ldfld      float32 Microsoft.Xna.Framework.Vector2::Y
  IL_0037:  br.s       IL_003f
  IL_0039:  ldarg.0
  IL_003a:  ldfld      float32 Microsoft.Xna.Framework.Vector2::Y
  IL_003f:  stfld      float32 Microsoft.Xna.Framework.Vector2::Y
  IL_0044:  ret
} // end of method Vector2::Min

和

.method public hidebysig static valuetype Microsoft.Xna.Framework.Vector2 
        Min(valuetype Microsoft.Xna.Framework.Vector2 value1,
            valuetype Microsoft.Xna.Framework.Vector2 value2) cil managed
{
  // Code size       80 (0x50)
  .maxstack  3
  .locals init (valuetype Microsoft.Xna.Framework.Vector2 V_0)
  IL_0000:  ldloca.s   V_0
  IL_0002:  ldarga.s   value1
  IL_0004:  ldfld      float32 Microsoft.Xna.Framework.Vector2::X
  IL_0009:  ldarga.s   value2
  IL_000b:  ldfld      float32 Microsoft.Xna.Framework.Vector2::X
  IL_0010:  blt.s      IL_001b
  IL_0012:  ldarga.s   value2
  IL_0014:  ldfld      float32 Microsoft.Xna.Framework.Vector2::X
  IL_0019:  br.s       IL_0022
  IL_001b:  ldarga.s   value1
  IL_001d:  ldfld      float32 Microsoft.Xna.Framework.Vector2::X
  IL_0022:  stfld      float32 Microsoft.Xna.Framework.Vector2::X
  IL_0027:  ldloca.s   V_0
  IL_0029:  ldarga.s   value1
  IL_002b:  ldfld      float32 Microsoft.Xna.Framework.Vector2::Y
  IL_0030:  ldarga.s   value2
  IL_0032:  ldfld      float32 Microsoft.Xna.Framework.Vector2::Y
  IL_0037:  blt.s      IL_0042
  IL_0039:  ldarga.s   value2
  IL_003b:  ldfld      float32 Microsoft.Xna.Framework.Vector2::Y
  IL_0040:  br.s       IL_0049
  IL_0042:  ldarga.s   value1
  IL_0044:  ldfld      float32 Microsoft.Xna.Framework.Vector2::Y
  IL_0049:  stfld      float32 Microsoft.Xna.Framework.Vector2::Y
  IL_004e:  ldloc.0
  IL_004f:  ret
} // end of method Vector2::Min

似乎开销是由临时矢量引起的。我也尝试了 1GHz WP 7.5 设备：

• 1979
年
• 1677
年

一个数量级的刻度数 迭代次数较小。