Scope Functions Flashcards

KOTLIN › Language Idioms

What does apply return and how does it reference the object?

apply returns the context object itself (the receiver) and references it as this. Ideal for configuring an object and returning it.

What does also return and how does it reference the object?

also returns the context object itself and references it as it. Used for side effects like logging or validation within a chain.

What does let return and how does it reference the object?

let returns the lambda result and references the object as it. Common for null-checks via ?.let and transforming a value.

How do run and with differ from let in their return value and reference?

run and with both return the lambda result but reference the object as this (receiver), whereas let returns the lambda result but uses it.

Which scope functions return the context object rather than the lambda result?

Only apply and also return the context object. let, run, and with return the lambda result.

Why is ?.let preferred for null-checks?

The safe call ?.let runs the lambda only when the receiver is non-null, and inside it the value is smart-cast to non-null, avoiding a separate null guard.

What is the difference between run as an extension and the non-extension run?

Extension run is called on an object (obj.run { }) with this as receiver. Non-extension run takes no object and just executes a block of statements where an expression is needed.

When would you choose apply over also for object configuration?

Use apply when assigning the object's own properties (this lets you write them bare). Use also when you need the object as an argument, e.g. passing it to a logger as it.

What is the key difference between with and run?

Both use this and return the lambda result, but with is a non-extension taking the object as an argument (with(obj){ }), while run is an extension called on a nullable-safe receiver (obj.run{ }).

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