Indexer with custom types in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an indexer in C#?

An indexer allows an object to be indexed like an array, using the square bracket syntax []. It lets you access elements inside a class or struct using a key or index.

intermediate

Can indexers use custom types as their index parameter?

Yes, indexers can use any type as the index parameter, including custom classes or structs, as long as the type supports equality comparison if needed.

intermediate

How do you declare an indexer with a custom type as the index in C#?

You declare the indexer with the custom type inside the square brackets. For example: <br>public string this[MyKey key] { get { ... } set { ... } }

intermediate

Why might you use a custom type as an indexer key instead of a simple type like int or string?

Using a custom type allows you to use complex keys that group multiple values or have special behavior, making your code clearer and more organized.

advanced

What must a custom type used as an indexer key implement or override for correct behavior?

It should override Equals() and GetHashCode() methods to ensure correct comparison and hashing, especially if used in collections like dictionaries internally.

Which of the following can be used as an index parameter in a C# indexer?

A Only int and string types

B Any type, including custom classes or structs

C Only primitive types like int, double, bool

D Only types that implement IEnumerable

C# indexers can use any type as the index parameter, including custom types.

What keyword is used to declare an indexer in a C# class?

A index

B get

C set

D this

The keyword 'this' is used to declare an indexer in C#.

If you use a custom type as an indexer key, what should you override for correct key comparison?

A ToString()

B CompareTo()

C Equals() and GetHashCode()

D Finalize()

Overriding Equals() and GetHashCode() ensures correct comparison and hashing of keys.

What is the return type of an indexer in C#?

A Any type defined by the indexer

B Always int

C Always string

D void

The return type of an indexer can be any type you define.

Which of these is a valid indexer declaration using a custom type 'Key'?

A public string this[Key key] { get; set; }

B public void this[Key key] { get; set; }

C public Key this[string index] { get; set; }

D public int this[int index] { get; set; }

An indexer must have a return type other than void; option A is valid with a custom type as index.

Explain how to create an indexer in C# that uses a custom class as the index parameter.

Think about how you access elements like an array but with your own key type.

Why is it important to override Equals() and GetHashCode() in a custom type used as an indexer key?

Consider what happens when you look up keys in a dictionary.