## What is covariance and contravariance in generic?

Covariance and contravariance are terms that refer to the ability to use a more derived type (more specific) or a less derived type (less specific) than originally specified. Generic type parameters support covariance and contravariance to provide greater flexibility in assigning and using generic types.

**What is the difference between covariance and contravariance?**

A device which can compare two Animals can also compare two Tigers, but a device which can compare two Tigers cannot necessarily compare any two Animals. So that’s the difference between covariance and contravariance in C# 4. Covariance preserves the direction of assignability. Contravariance reverses it.

### What is the use of covariance and contravariance?

In C#, covariance and contravariance enable implicit reference conversion for array types, delegate types, and generic type arguments. Covariance preserves assignment compatibility and contravariance reverses it.

**What is covariance and contravariance in Java?**

Covariance can be translated as “different in the same direction,” or with-different, whereas contravariance means “different in the opposite direction,” or against-different. Covariant and contravariant types are not the same, but there is a correlation between them. The names imply the direction of the correlation.

#### How is covariance calculated?

Covariance is calculated by analyzing at-return surprises (standard deviations from the expected return) or by multiplying the correlation between the two variables by the standard deviation of each variable.

**What does Contravariance mean?**

In differential geometry, the components of a vector relative to a basis of the tangent bundle are covariant if they change with the same linear transformation as a change of basis. They are contravariant if they change by the inverse transformation.

## What is covariance stackoverflow?

Covariance: Covariance lets you to pass a derived type object where a base type object is expected Covariance can be applied on delegate, generic, array, interface, etc.

**What is generic classes in Java?**

Java Generics is a set of related methods or a set of similar types. Generics allow types Integer, String, or even user-defined types to be passed as a parameter to classes, methods, or interfaces. Generics are mostly used by classes like HashSet or HashMap.

### What is array covariance?

#572 – Why Array Covariance Is Called Covariance Array covariance in C# allows you to assign an array of instances of a derived class to a variable whose type is an array of instances of the base class.

**What does covariance tell?**

Covariance indicates the relationship of two variables whenever one variable changes. If an increase in one variable results in an increase in the other variable, both variables are said to have a positive covariance. Both variables move together in the same direction when they change.

#### Why do we calculate covariance?

Covariance is a statistical tool that is used to determine the relationship between the movement of two asset prices. When two stocks tend to move together, they are seen as having a positive covariance; when they move inversely, the covariance is negative.

**How are type parameters related to covariance and contravariance?**

Types with more than one type parameter may specify different variances on each type parameter. For example, the delegate type Func represents a function with a contravariant input parameter of type T and a covariant return value of type TResult. The typing rules for interface variance ensure type safety.

## Is it safe to use covariance in an array?

Covariance for arrays enables implicit conversion of an array of a more derived type to an array of a less derived type. But this operation is not type safe, as shown in the following code example.

**When to use covariance and contravariance in delegate?**

Covariance in delegates allows flexiblity in the return type of delegate methods. As you can see in the above example, delegate expects a return type of small (base class) but we can still assign Method1 that returns Big (derived class) and also Method2 that has same signature as delegate expects.

### Why do we use covariance and contravariance in Computer Science?

Covariance and contravariance (computer science) In order to keep the type system simple and allow useful programs, a language may treat a type constructor as invariant even if it would be safe to consider it variant, or treat it as covariant even though that could violate type safety.