Covariance vs. Contravariance: How Do They Differ in Programming?

In -depth understanding of collaboration and inverting: The key differences in programming

Coordination and inverter are two vital concepts in programming. They define how the functions are applied to different types of objects to ensure type security and flexibility.

Cooperation: Keep assignment compatibility

Coordination is suitable for mapping functions that maintain the compatibility of objects. This means that if the object of the type X can be assigned to the object of the type Y, the result of applying the mapping function to X can always be assigned to the result of applying the function to Y.

For example, consider a set of animals, including Animal, Tiger, FRUIT and Banana. By defining a mapping function from Animal to IenuMerable

, we get the following types:

Under the relationship between assignment and compatibility, we have Tiger ⇒ Animal and Banana ⇒ FRUIT. The application mapping function maintains this compatibility, and the result is IenuMerable

⇒ INUMERABLE

<code>{ Animal, 
  Tiger, 
  Fruit, 
  Banana } → { IEnumerable<animal>, 
  IEnumerable<tiger>, 
  IEnumerable<fruit>, 
  IEnumerable<banana> }</banana></fruit></tiger></animal></code>

and INUMERABLE

⇒ INUMERABLE . Reverse: Reverse assignment compatibility relationship

Different from the coordination, the inverter reverses the assignment compatibility relationship. This means that if the object of the type X can be assigned to the object of the type Y, the result of applying the mapping function to Y can be assigned to the result of the application of the function to X. Consider the collection of IComparable type:

In C#, we observe the following compatible relationship:

<code>{ IComparable<tiger>, 
  IComparable<animal>, 
  IComparable<fruit>, 
  IComparable<banana> } → { IC<tiger>, 
  IC<animal>, 
  IC<fruit>, 
  IC<banana> }</banana></fruit></animal></tiger></banana></fruit></animal></tiger></code>

The application mapping function reverses the direction of compatibility. As a result, IC

⇐ ic

, IC

<code>Animal ⇒ Tiger
Tiger ⇒ Tiger
Banana ⇒ Banana
Fruit ⇒ Banana
Fruit ⇒ Fruit</code>

⇐ ic

, and so on. This behavior ensures that the device that can compare Animal can compare the Tiger, otherwise it is not the other. Summary

The difference between understanding the coordination and the inverter is essential for effective use of programming languages. The coordinating change maintains the direction of the assignment, while the inverter reverses it. These concepts allow high -efficiency and flexible operations of various types of objects to ensure type security and procedure correctness.

The above is the detailed content of Covariance vs. Contravariance: How Do They Differ in Programming?. For more information, please follow other related articles on the PHP Chinese website!