游戏里面对于异步的处理经常会用到Coroutine，很多时候Coroutine并不是一次处理或一帧内处理完毕，所以经常会用到yield return：
yield return new WaitForEndOfFrame()
yield return new WaitForFixedUpdate();
yield return new WaitForSeconds(1.0f);
众所周知，C#是带有GC的语言，在yield return中出现了new也就意味着可能会带来一次GC，那么每一次的yield return都会产生新对象。在Unity中，我们可以保存对象的方式来避免对象的分配。
public static class Yielders
{
class FloatComparer : IEqualityComparer<float>
{
bool IEqualityComparer<float>.Equals(float x, float y)
{
return x == y;
}
int IEqualityComparer<float>.GetHashCode(float obj)
{
return obj.GetHashCode();
}
}
static WaitForEndOfFrame _endOfFrame = new WaitForEndOfFrame();
public static WaitForEndOfFrame EndOfFrame
{
get { _endOfFrame; }
}
static WaitForFixedUpdate _fixedUpdate = new WaitForFixedUpdate();
public static WaitForFixedUpdate FixedUpdate
{
get { _fixedUpdate; }
}
static Dictionary<float, WaitForSeconds> _timeInterval = new Dictionary<float, WaitForSeconds>(100, new FloatComparer());
public static WaitForSeconds GetWaitForSeconds(float seconds)
{
WaitForSeconds wfs;
if (!_timeInterval.TryGetValue(seconds, out wfs))
_timeInterval.Add(seconds, wfs = new WaitForSeconds(seconds));
return wfs;
}
}