OC_自动引用计数器_0x07
属性声明的属性与所有权修饰符的对应关系
assign __unsafe_unretained
copy __strong
retain __strong
strong __strong
unsafe_unretained __unsafe_unretained
weak __weak
属性声明的属性与所有权修饰符的对应关系
assign __unsafe_unretained
copy __strong
retain __strong
strong __strong
unsafe_unretained __unsafe_unretained
weak __weak