Collection in C#

The collection classes in the System.Collections namespace are generally weakly typed which implies that they store everything internally as System.Object. ArrayList and Hashtable are examples of such classes.

This means that, when retrieving elements of the collection, you have to cast them to their actual type before you can use them as such.

It also means that when you store value types (int, double, char, bool etc) they have to be boxed on the heap when storing them and unboxed (by casting) when you retrieve them, which is a relatively slow process.

In contrast the generic collection classes in the System.Collections.Generic namespace are strongly typed which implies that they store everything internally as its actual type. List and Dictionary are examples of such classes and the generic analogs of ArrayList and Hashtable.

This means that no casting is required when retrieving elements from generic collections and no boxing is required for value types which makes them more performant in that respect.

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Vulpes14y ago
The collection classes in the System.Collections namespace are generally weakly typed which implies that they store everything internally as System.Object. ArrayList and Hashtable are examples of such classes.

This means that, when retrieving elements of the collection, you have to cast them to their actual type before you can use them as such.

It also means that when you store value types (int, double, char, bool etc) they have to be boxed on the heap when storing them and unboxed (by casting) when you retrieve them, which is a relatively slow process.

In contrast the generic collection classes in the System.Collections.Generic namespace are strongly typed which implies that they store everything internally as its actual type. List and Dictionary are examples of such classes and the generic analogs of ArrayList and Hashtable.

This means that no casting is required when retrieving elements from generic collections and no boxing is required for value types which makes them more performant in that respect.