Type patterns in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a type pattern in C#?

A type pattern checks if an object is of a specific type and, if so, allows you to use it as that type in a safe way.

beginner

How do you use a type pattern with the is keyword?

You write if (obj is TypeName variableName). This checks if obj is of TypeName and, if true, assigns it to variableName for use inside the block.

beginner

What happens if the type pattern check fails?

If the object is not of the specified type, the pattern check returns false and the variable is not assigned.

intermediate

Can you use type patterns in a switch statement?

Yes! You can match the type of a variable in switch cases using type patterns, making code clearer and safer.

beginner

Example: What does this code do?<br>

if (obj is string s) { Console.WriteLine(s.Length); }

It checks if obj is a string. If yes, it assigns it to s and prints the length of the string.

What does the type pattern if (obj is int number) do?

A Checks if obj is an int and assigns it to number if true

B Converts obj to int without checking

C Always assigns obj to number

D Checks if obj is null

The pattern checks the type and assigns only if obj is an int.

Which keyword is used with type patterns to check an object's type?

A is

B typeof

C switch

D as

The 'is' keyword is used to check type patterns.

What happens if the type pattern check fails?

A The variable is assigned default value

B The code throws an exception

C The variable is assigned null

D The condition is false and variable is not assigned

If the object is not of the specified type, the check returns false and the variable is not assigned.

Can type patterns be used inside a switch statement?

A No, only if statements

B Yes, to match types in cases

C Only with enums

D Only with strings

Type patterns can be used in switch cases to match object types.

What is the benefit of using type patterns?

A They automatically convert types

B They replace all casts

C They allow safe type checking and variable assignment

D They improve performance by skipping checks

Type patterns let you check types safely and use the variable if the check passes.

Explain how type patterns work with the 'is' keyword in C#.

Think about how you check and use an object's type in one step.

Describe how type patterns can be used in a switch statement and why that is useful.

Consider how switch can handle different types safely.