Lazy evaluation vs eager evaluation in Kotlin - When to Use Which

The Big Idea

What if your program could skip all the boring work and jump straight to the answer?

The Scenario

Imagine you have a list of 1,000 numbers and you want to find the first number that meets a certain condition. If you check every number right away, even those you don't need, it wastes time and effort.

The Problem

Checking all items immediately (eager evaluation) means you do a lot of unnecessary work. It's like reading every page of a book to find one sentence. This slows down your program and uses more memory.

The Solution

Lazy evaluation waits to do the work until it's really needed. It's like flipping pages only until you find the sentence you want. This saves time and resources by avoiding extra work.

Before vs After

✗ Before

val result = list.map { it * 2 }.filter { it > 10 }.first()

✓ After

val result = list.asSequence().map { it * 2 }.filter { it > 10 }.first()

What It Enables

Lazy evaluation lets your program run faster and use less memory by doing only the work that matters, exactly when it matters.

Real Life Example

When loading images in an app, lazy evaluation means images load only when you scroll to them, not all at once, making the app faster and smoother.

Key Takeaways

Manual eager evaluation does all work upfront, wasting time and memory.

Lazy evaluation delays work until needed, improving efficiency.

Using lazy sequences in Kotlin helps write faster, cleaner code.