Named captures in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a named capture in Ruby regular expressions?

A named capture lets you give a name to a part of a regular expression match, so you can access it by that name instead of by number.

beginner

How do you define a named capture group in a Ruby regex?

Use the syntax (?<name>pattern) where name is the capture's name and pattern is what you want to match.

beginner

How do you access the value of a named capture after a match in Ruby?

You can use MatchData#[] with the capture name as a symbol or string, like match[:name] or match["name"].

beginner

What does this Ruby code output?<br>

text = "Name: Alice"
if text =~ /Name: (?<user>\w+)/
  puts "User is #{Regexp.last_match[:user]}"
end

It outputs: User is Alice because the named capture user matches "Alice" and is accessed with Regexp.last_match[:user].

beginner

Why are named captures useful compared to numbered captures?

Named captures make code easier to read and maintain because you use meaningful names instead of numbers, which can be confusing especially with many groups.

Which syntax defines a named capture group in Ruby regex?

A (name:pattern)

B (?<name>pattern)

C (name=pattern)

D (pattern?<name>)

The correct syntax for named captures in Ruby is (?pattern).

How do you access a named capture called 'id' from a MatchData object named 'match'?

A match.id

B match.get('id')

C match['id']()

D match[:id]

You access named captures using square brackets with the name as a symbol or string, like match[:id].

What will this code print?<br>

text = "Age: 30"
if text =~ /Age: (?<age>\d+)/
  puts Regexp.last_match[:age]
end

A age

B Age

C 30

D Error

The named capture 'age' matches '30', so it prints '30'.

Why might you prefer named captures over numbered captures?

A They make code easier to understand by using meaningful names.

B They run faster than numbered captures.

C They allow matching multiple patterns at once.

D They automatically convert strings to numbers.

Named captures improve readability by using descriptive names instead of numbers.

Which of the following provides access to the MatchData object after a successful regex match in Ruby?

A All of the above

B Regexp.last_match

C String#match

D =~ operator

All these can provide MatchData: =~ operator sets Regexp.last_match, and String#match returns MatchData.

Explain how to create and use named captures in Ruby regular expressions.

Think about the <code>(?<name>pattern)</code> syntax and accessing with MatchData.

Describe the benefits of using named captures instead of numbered captures in Ruby regex.

Consider how meaningful names help when you have many groups.