Question

为什么不能直接更改transform.position.x的值

Answer 1

　　这个问题我搞错了，这里修正一下。这是c#中的结构体当作返回值的问题，结构体是值类型，而值传递是复制传递，所以返回的值不是原来的值了，对此返回值的修改是无效的，所以编译器就从源头上禁止了这样的操作。

　　unity论坛上有这个问题的讨论
　　The reason you can't directly alter the position vector is because it's actually a copy, not the actual position stored on the transform.

　　transform.position <--- returns a copy of the position
　　transform.position.x <--- the "x" value of the copy
　　transform.position.x = 7.0f <--- sets the "x" value on the copy

　　C# throws an error because you're setting the "x" value on a copy, which is then destroyed. It's a pointless line that if the compiler didn't pick up on it, could cause a tonne of hair pulling.

　　UnityScript gets around this when it compiles by converting your code and firing the C# setter:
　　transform.position.x = 7.0f
　　when compiled in UnityScript, translates (more or less) to:
　　var tempVector : Vector3 = transform.position;
　　tempVector.x = 7.0f;
　　transform.position = tempVector;

　　You can infer that because if you replicate this with a custom C# class, you can track as the getters/setters are invoked.