ios动态创建类Class

动态创建类Class,动态添加Class成员变量与成员函数,动态变量赋值与取值，动态函数调用等方法

a.使用objc_allocateClassPair创建一个类Class
    const char * className = "Calculator";
    Class kclass = objc_getClass(className);
    if (!kclass) 
    {
       Class superClass = [NSObject class]; 
       kclass = objc_allocateClassPair(superClass, className, 0);
    }

b.使用class_addIvar添加一个成员变量
    NSUInteger size;
    NSUInteger alignment;
    NSGetSizeAndAlignment("*", &size, &alignment);
    class_addIvar(kclass, "expression", size, alignment, "*");


    注:
    1.type定义参考:    [instance performSelector:@selector(getExpressionFormula)];