Question

There are other questions such as KeyValuePair vs IDictionary, but I feel this one differs slightly.

NameValueCollection takes a string key and string value.

KeyValuePair is like a dictionary, you tell it what type the key and value is.

I don’t understand why NameValueCollection exists. Initializing a KeyValuePair with string types seems sufficient. I also noticed that NameValueCollection has some more methods available to it, but again why not merge both classes into one?

Answer 1

A KeyValuePair not like a dictionary. It is simply a Tuple containing the Key and the Value.

NameValueCollection is wrapper over what amounts to a IList<KeyValuePair<string,IList<string>>> (note that NameValueCollection predates generics) – operations like Get(string) are O(n) and items can be fetched by index and each Key maps to one or more Values (this differs from a Dictionary<string,string>).

A reason for this is explained in the NameValueCollection documentation:

This class can be used for headers, query strings and form data.

The newer “replacement” data-structure with some similar behavior for NameValueCollection is Lookup<string,string>. (However, it doesn’t directly support the same operations as is immutable as spender notes.)

Happy coding.