Why Can't a `List` Be Assigned to a `List` Variable in C#?

Why can't the

object value variable? List<string></string> List<object></object> In C#, try to assign objects to

variables can cause errors during compilation. This operation is not allowed even if it is explicitly converted. Let's explore the principle behind it:

List<string></string> Consider the following scene: List<object></object>

If this conversion can be successfully executed, what will happen if you add a type of

to the

List<string> sl = new List<string>();
List<object> ol;
ol = sl; // 产生编译时错误

list? This will create an inconsistency in the

list, because the ol list expects only the string. When traversing the list, encountering the Foo instance will cause the class conversion abnormality, indicating that it cannot be converted into a string. sl sl On the contrary, the conversion from to sl may be useful. By converting from a more general class () to a more specific class (Foo), it ensures that adding any elements to the string list will not violate the constraints of the object list. However, C# may not support this type of conversion.

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