Are there any restrictions on the use of keys in a dictionary?

In C#, keys in a dictionary (Dictionary<TKey, TValue>) must meet the following requirements:

• Uniqueness: each key must be unique within the dictionary. Attempting to add a duplicate will throw an exception.

• Hashability: the key type must correctly implement the GetHashCode() and Equals() methods so that the dictionary can efficiently find elements.

• Immutability of the key: it is recommended to use immutable types as keys so that the hash code and equality do not change after being added to the dictionary. Changing a key can lead to loss of access to the element.

For example, strings (string) are often used as keys because they are immutable and correctly implement the necessary methods.

If custom types are used as keys, Equals and GetHashCode should be overridden for the dictionary to work correctly.