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| Ligne 9 : | Ligne 9 : | ||
= Assignment compatibility = | = Assignment compatibility = | ||
Allow an object of a more derived type (child class, ex: string) to be assigned to an object of a less derived type (parent class, ex: object). | |||
<kode lang='cs'> | <kode lang='cs'> | ||
string s = "test"; | string s = "test"; | ||
object o = s; | |||
</kode> | |||
= Covariance = | |||
object | Allow a generic object of child class type (ex: string) to be assigned to a generic object of parent class type (ex: object). | ||
{{info | It works only with covariant interface}} | |||
<kode lang='cs'> | |||
var strings = new List<string>(); | |||
List<object> objects = strings; // Cannot convert type List<string> to List<object> because there is no covariance with List<T> | |||
IList<object> objects = strings; // Cannot implicitly convert type List<string> to IList<object>. An explicit conversion exists | |||
IEnumerable<object> objects = strings; // There is covariance with IEnumerable<T> | |||
var objects = (IList<object>)strings; // There is covariance with IList<T> | |||
</kode> | </kode> | ||
Version du 26 mars 2024 à 14:51
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Description
Covariance enable implicit reference conversion for array types, delegate types, and generic type arguments.
Covariance preserves assignment compatibility and contravariance reverses it.
Assignment compatibility
Allow an object of a more derived type (child class, ex: string) to be assigned to an object of a less derived type (parent class, ex: object).
|
string s = "test"; object o = s; |
Covariance
Allow a generic object of child class type (ex: string) to be assigned to a generic object of parent class type (ex: object).
 |
It works only with covariant interface |
|
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var strings = new List<string>(); List<object> objects = strings; // Cannot convert type List<string> to List<object> because there is no covariance with List<T> IList<object> objects = strings; // Cannot implicitly convert type List<string> to IList<object>. An explicit conversion exists IEnumerable<object> objects = strings; // There is covariance with IEnumerable<T> var objects = (IList<object>)strings; // There is covariance with IList<T> |
