What is Dart's equivalent to Kotlin's let?

Question

Recently I've been delving into Flutter's ecosystem and Dart has proven itself a neat and simple language.

Currently, I am looking for a best practice to run methods if an optional variable is not null.

In other words, I am looking for something in Dart that is like Kotlin's let operator :

variable?.let {
    doStuff();
    doABitMoreStuff();
    logStuff();
}

Anyone got any ideas or best practices around this?

I've looked into Dart's documentation and have found nothing that would fit my requirements.

King regards,

Answer 1

With the new Dart extension functions, we can define:

extension ObjectExt<T> on T {
  R let<R>(R Function(T that) op) => op(this);
}

This will allow to write x.let(f) instead of f(x).

Answer 2

Dart's equivalent would be a null-aware cascade operator: The Dart approach would be a to use a null-aware cascade:

SomeType? variable = ...

variable
   ?..doStuff()
    ..doABitMoreStuff()
    ..logStuff();

The null-aware cascade works like the normal cascade, except that if the receiver value is null, it does nothing.

---

You could make your own using a static function though:

typedef T LetCallback<T>(T value);

T let<T>(T value, LetCallback<T> cb) {
  if (value != null) {
    return cb(value);
  }
}

Then used like that:

let<MyClass>(foo, (it) {

})

Answer 3

We can do it with Dart 2.6 or later.

extension ScopeFunctionsForObject<T extends Object> on T {
  ReturnType let<ReturnType>(ReturnType operation_for(T self)) {
    return operation_for(this);
  }
}

usage: https://github.com/YusukeIwaki/dart-kotlin_flavor#let