Covariance vs. Contravariance: What's the Difference and How Are They Used in C#?

In -depth understanding of the coordination and inversion in C#

The concepts of coordination and inverting are often confusing. This article will explore the essence of collaborative and inverse, and clarify its usage through specific examples.

What is a coordinated change?

Coordination is a characteristic of the refreshment function to maintain the direction of assignment compatibility. Suppose we have a mapping from collection A to collection B, which is recorded as A → B. If A and B are correlated through the relationship R, where the AR B, when ARB contains f (a) RF (b), the mapping is a coordinated change. For example, the mapping T → Ienumeability

converts the type T to its corresponding IenumeRable collection type. In C#, this mapping is coordinated, because the object of the type T can be assigned to the object of the type Ienumerable

, so you can use IenuMerable

where you need Ienumeration & LT; derived type & gt; & lt;/derived type & gt;

Reverse

On the other hand, the inverter reverses the direction of assignment compatibility. Reverse mapping function T → C

(where C indicates a comparison or standard type) maintains the relationship R, but reverse its direction. In other words, if AR B, C ⇐ C

.

For example, Icomparable Compare the two types T objects, mapping T → Icomparable is inverted. You can use iComparable & LT; derived type & gt; instances that require iComparable & lt; base type & gt;, because the derived type is more specific than its base type, and can perform the same comparison as the base type. & lt;/base type & gt; & lt;/derived type & gt;

The coordinated and inverter in the c# In short, the coordinated change maintains the direction of assignment, and the inverted reversal assignment direction. In C#, the collaborative type (such as Ienumeration ) allows the derived type to replace the base type, while the inverter type (such as IComparable

) reverses this relationship, allowing use of the derived type at the base type position. Understanding these concepts can help developers write more flexible and more efficient code.

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