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

Recall & Review

beginner

What is a positional pattern in C#?

A positional pattern lets you match an object by its position in a Deconstruct method or a record, checking its parts directly in a concise way.

beginner

How do you use positional patterns with records in C#?

You write the record name followed by parentheses with variables to match each part, like: RecordName(var1, var2).

intermediate

What method must a class have to support positional patterns?

It must have a Deconstruct method that outputs the parts you want to match.

beginner

Example: How to match a Point record with positional pattern to get X and Y?

Use case Point(var x, var y): inside a switch or if to get X and Y values from the Point.

intermediate

What happens if the number of variables in a positional pattern does not match the Deconstruct method?

The code will not compile because the pattern expects the exact number of parts to match.

Which method enables positional patterns in a class?

A ToString

B Deconstruct

C Equals

D GetHashCode

The Deconstruct method defines how to split an object into parts for positional pattern matching.

How do you write a positional pattern for a record named Point with two parts?

A Point->(x, y)

B Point[x, y]

C Point{x, y}

D Point(var x, var y)

Positional patterns use parentheses with variables inside after the type name.

What will happen if you use fewer variables than the Deconstruct method parts in a positional pattern?

A It throws runtime exception

B It matches only the first parts

C Compilation error

D It ignores extra parts

The compiler requires the number of variables to match the Deconstruct method exactly.

Positional patterns are mainly used inside which C# construct?

A switch expressions

B for loops

C try-catch blocks

D class declarations

Switch expressions commonly use positional patterns to match object parts.

Which C# feature introduced positional patterns?

A C# 9.0

B C# 7.0

C C# 8.0

D C# 10.0

Positional patterns were introduced in C# 9.0 along with records.

Explain how positional patterns work with records and Deconstruct methods in C#.

Think about how you break down an object into pieces to check them.

Describe what happens if the number of variables in a positional pattern does not match the Deconstruct method.

Consider how strict the compiler is about matching parts.