Swift defines two kinds of initializers for class types to help ensure all stored properties receive an initial value. These are known as designated initializers and convenience initializers.

Designated：指定的；特指的

全初始化與部分初始化

Designated Initializers and Convenience Initializers

Designated initializers are the primary initializers

Convenience initializers are secondary, supporting initializers for a class. You can define a convenience initializer to call a designated initializer from the same class as the convenience initializer with some of the designated initializer’s parameters set to default values.

swift語言點評十七-Designated Initializers and Convenience Initializers