Collections之Pointer Collections ：指针集合类

• 1. NSPointerArray
• 1. NSHashTable
• 1. NSMapTable

1.NSPointerFunctionsOptions

Defines the memory and personality options for an NSPointerFunctions object.

• NSPointerFunctionsMachVirtualMemory

• NSPointerFunctionsMallocMemory

     Use free() on removal, calloc() on copy in.
  

• NSPointerFunctionsOpaqueMemory

• NSPointerFunctionsStrongMemory

• NSPointerFunctionsWeakMemory

    Uses weak read and write barriers appropriate for ARC or GC. Using NSPointerFunctionsWeakMemory object references will turn to NULL on last release.
  

• NSMapTableStrongMemory

  Equivalent to NSPointerFunctionsStrongMemory .

• NSMapTableWeakMemory

    Equivalent to NSPointerFunctionsWeakMemory.
  

2. NSPointerArray/NSHashTable/NSMapTable

• 可以存储所有指针类型的数据包括nil
• 可以添加或删除nil values
• 可以弱引用或强引用对象。
• 添加元素时，性能很差。慎用！！！