下午在適配iPadUI的時候，用到了UIPopoverPresentationController,然后在轉屏的時候需要調用UIPopoverPresentationControllerDelegate來返回一個適配后的view和CGRect，這里先看下在OC里的寫法：
- (void)popoverPresentationController: (nonnull UIPopoverPresentationController *) popoverPresentationController willRepositionPopoverToRect:(inout nonnull CGRect *)rect inView:(inout UIView *__autoreleasing __nonnull * __nonnull)view { *view = self.someView; *rect = self.someView.bounds; }在OC里面你可以很方便的修改這里的參數值來返回正確的指針地址，但是在swift里面方法是這樣子的：
func popoverPresentationController( popoverPresentationController:UIPopoverPresentationController, willRepositionPopoverToRect rect: UnsafeMutablePointer<CGRect>, inView view: AutoreleasingUnsafeMutablePointer<UIView?>) { // What to do here? }UnsafeMutablePointer和AutoreleasingUnsafeMutablePointer是什么鬼？這倆玩意要怎么返回值給他們？
先說結論：
在Swift里面rect.memory就是Objective-C里面的*rect
原因：
這兩個參數並不是swift本身的寫法混亂，而是為了讓swift和Cocoa和UIKit下的Objective-C和C的frameworks 相互轉換兼容，查閱apple的SDK你可以發現UnsafeMutablePointer就是一個結構體：
struct UnsafeMutablePointer<Memory>你可以把它看成一個Memory的指針，那現在再來看protocol里面的兩個參數：
UnsafeMutablePointer<CGRect>是一個CGRect的指針AutoreleasingUnsafeMutablePointer<UIView?>是一個可選View的指針
所以這里你可以通過它的memory屬性來訪問它的引用存儲值：
/// Access the underlying raw memory, getting and setting values.public var memory: Memory { get nonmutating set }例如：
// Objective-C assuming CGRect *rect; CGRect oldRect = *rect; *rect = newRect; // Swift assuming rect: UnsafeMutablePointer<CGRect> oldRect = rect.memory rect.memory = newRect簡單來說：在Swift里面rect.memory就是Objective-C里面的*rect
所以最后我們可以在Swift里面這么寫：
func popoverPresentationController( popoverPresentationController:UIPopoverPresentationController, willRepositionPopoverToRect rect: UnsafeMutablePointer<CGRect>, inView view: AutoreleasingUnsafeMutablePointer<UIView?>) { view.memory = someView rect.memory = someView.bounds }參考：
Swift Standard Library Reference - UnsafeMutablePointer Structure Reference
How to Dereference an Unsafe Mutable Pointer in Swift