Lazy enumerators in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a lazy enumerator in Ruby?

A lazy enumerator in Ruby is an enumerator that delays computation until the values are needed. It helps to work efficiently with large or infinite collections by processing elements one at a time instead of all at once.

beginner

How do you create a lazy enumerator from an array in Ruby?

You can create a lazy enumerator by calling lazy on an enumerable object, like an array. For example: [1, 2, 3].lazy returns a lazy enumerator.

intermediate

Why use lazy enumerators instead of regular enumerators?

Lazy enumerators avoid computing all elements at once. This saves memory and time when working with large or infinite sequences, because values are generated only when needed.

intermediate

What happens if you chain methods on a lazy enumerator?

When you chain methods on a lazy enumerator, each method call is recorded but not executed immediately. The computation happens only when you force evaluation, like calling force or converting to an array.

beginner

How do you force a lazy enumerator to compute its values?

You can force a lazy enumerator to compute its values by calling force or converting it to an array with to_a. This triggers the actual processing of elements.

What does calling lazy on an enumerable do in Ruby?

A Removes duplicates from the enumerable

B Immediately processes all elements

C Converts the enumerable to a string

D Creates a lazy enumerator that delays computation

Calling lazy creates a lazy enumerator that delays processing elements until needed.

Which method forces a lazy enumerator to evaluate all its elements?

A lazy

B map

C force

D select

The force method triggers evaluation of all elements in a lazy enumerator.

Why are lazy enumerators useful for infinite sequences?

A They store all elements in memory

B They process elements one at a time on demand

C They convert sequences to arrays immediately

D They sort the sequence automatically

Lazy enumerators process elements only when needed, making infinite sequences manageable.

What happens when you chain multiple methods on a lazy enumerator?

A Methods are recorded but not executed until forced

B All methods run immediately

C The enumerator converts to an array

D The enumerator raises an error

Chained methods on a lazy enumerator are recorded and executed only when evaluation is forced.

How do you create a lazy enumerator from a range in Ruby?

A (1..10).lazy

B (1..10).to_a

C (1..10).map

D (1..10).select

Calling lazy on a range creates a lazy enumerator.

Explain what a lazy enumerator is and why it is useful in Ruby.

Think about how lazy enumerators handle big lists or endless sequences.

Describe how method chaining works with lazy enumerators and how to trigger their evaluation.

Consider what happens when you add multiple steps before getting results.