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What is the difference between a List of KeyValuePair and a Dictionary for the same types? Is there an appropriate time to use one or the other?
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KeyValuePair is the unit of data stored in a Hashtable (or Dictionary ). They are not equivalent to each other. A key value pair contains a single key and a single value. A dictionary or hashtable contains a mapping of many keys to their associated values.
Dictionary is generic type that contains a collection of key-value pairs. Dictionary is fast for lookup operations, because is using hash function internally. That means, all the keys must be unique in dictionary.
A key-value pair (KVP) is a set of two linked data items: a key, which is a unique identifier for some item of data, and the value, which is either the data that is identified or a pointer to the location of that data. Key-value pairs are frequently used in lookup tables, hash tables and configuration files.
In Hashtable, you can store key/value pairs of the same type or of the different type. In Dictionary, you can store key/value pairs of same type. In Hashtable, there is no need to specify the type of the key and value. In Dictionary, you must specify the type of key and value.
When you don't need fast lookups on key - maintaining the hashtable used by Dictionary has a certain overhead.
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In short, the list does not enforce uniqueness of the key, so if you need that semantic then that's what you should use.
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