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

Recall & Review

beginner

What is a list pattern in C#?

A list pattern in C# is a way to match elements inside a list or array by their order and values. It lets you check if a list has specific elements in a certain sequence.

beginner

How do you match the first two elements of a list using list patterns?

You write a pattern like [var first, var second, ..]. This matches a list where the first element is stored in first, the second in second, and .. means any remaining elements.

beginner

What does the .. symbol mean in a list pattern?

The .. symbol means 'match the rest of the list'. It allows the pattern to match lists longer than the elements explicitly listed.

intermediate

Can list patterns be used to check for an exact list length?

Yes. If you write a pattern without .., like [1, 2, 3], it matches only lists with exactly three elements: 1, 2, and 3 in order.

intermediate

Give an example of using list patterns in a switch expression.

Example:<br>

return list switch {
  [1, 2, 3] => "Exact match",
  [1, 2, ..] => "Starts with 1, 2",
  _ => "Other"
};

This checks the list and returns a string based on the pattern matched.

What does the list pattern [var x, var y, ..] match?

A A list with exactly three elements

B A list with exactly two elements

C A list with no elements

D A list with at least two elements, capturing the first two

The pattern matches lists with two or more elements, capturing the first two into variables x and y, and the rest is ignored by '..'.

Which list pattern matches only a list with exactly three elements 1, 2, and 3?

A [1, 2, 3]

B [1, 2, ..]

C [.., 1, 2, 3]

D [1, .., 3]

The pattern [1, 2, 3] matches only lists with exactly those three elements in order.

In C# list patterns, what does the underscore (_) pattern mean?

A Match a list with one element

B Match an empty list only

C Match any list

D Match a list with exactly two elements

The underscore (_) is a discard pattern that matches anything, including any list.

Which of these is a valid list pattern in C#?

A {var a, var b, var c}

B [var a, var b, var c]

C (var a, var b, var c)

D <var a, var b, var c>

List patterns use square brackets [] to match elements in order.

What happens if you use [1, 2, ..] to match the list [1, 2]?

A It matches successfully

B It does not match

C It throws an error

D It matches only if the list has more than two elements

The pattern matches lists with two or more elements starting with 1 and 2. The list [1, 2] matches because '..' can match zero or more elements.

Explain how list patterns work in C# and how you can use them to check list contents.

Think about how you check items in a list one by one.

Describe a scenario where list patterns can simplify your code compared to traditional if-else checks.

Imagine you want to do different things based on the first few items in a list.