What data types are permissible as keys when working with dictionaries?

In C#, dictionary keys (Dictionary<TKey, TValue>) can be any types that meet the following requirements:

• Implement a proper Equals method for equality comparison.
• Implement the GetHashCode method for hash code calculation.

This is necessary for the dictionary to efficiently store and search for elements.

Examples of valid keys:

• Primitive types (int, string, Guid)
• User-defined classes and structs, if Equals and GetHashCode are overridden

Example of a user-defined key:

class Person
{
    public string Name { get; set; }
    public int Age { get; set; }

    public override bool Equals(object obj)
    {
        if (obj is Person other)
            return Name == other.Name && Age == other.Age;
        return false;
    }

    public override int GetHashCode()
    {
        return HashCode.Combine(Name, Age);
    }
}

var dict = new Dictionary<Person, string>();
dict[new Person { Name = "Alice", Age = 30 }] = "Developer";

If the key does not override these methods, the dictionary may not work correctly.