Table of contents
2.2 Differences from inheritance
1 union type
union type is OR relation
The joint type means that this variable can be of multiple types, for example a can be a number or a string
After using the joint type, changing to the specified type will not report an error
2 cross type
2.1 Basic use
The cross type is the relationship of and
The relationship between and cannot be a basic type, because an ordinary variable cannot be both a number and a string
2.2 Differences from inheritance
First of all, there is a logical difference. Inheritance is a father-son relationship, and the cross type is a brother relationship.
Let's look at the code level again. If you use cross types, sometimes it will automatically give you compatibility (not all cases, such as return values). For example, I defined fly() in both Bird and Person below. fly() has the same parameter a, one a defines a number, and the other a defines a character
At this time you define BP, the fly() of BP can be either a number or a character
When using inheritance, an error is reported directly, because the subclass cannot conflict with the parent class
