dart_scope_functions

dart_scope_functions is a Dart utility library that implements Kotlin-inspired scope functions. These functions provide a convenient way to execute a block of code within the context of an object, making the code more readable and expressive.

Features

• Execute blocks of code within the context of an object.
• Chain multiple operations on an object in a readable manner.
• Conditional operations on objects, including nullable types.

Installation

Add dart_scope_functions to your pubspec.yaml file:

dependencies:
  dart_scope_functions: latest

Then, run pub get to install the package.

Usage

Import the library:

import 'package:dart_scope_functions/dart_scope_functions.dart';

Example

void main() {
  var result = 'Hello'.also((it) {
    print(it); // Prints 'Hello'
  }).let((it) {
    return it.length;
  });

  print(result); // Prints 5

  String? nullableString = null;
  var defaultString = nullableString.withDefault('Default Value');
  print(defaultString); // Prints 'Default Value'

  var conditionResult = 42.takeIf((it) => it > 40);
  print(conditionResult); // Prints 42

  var runResult = run(() {
    return 'Running a block';
  });
  print(runResult); // Prints 'Running a block'
}

API

Extensions on Any Type [T]

T also(void Function(T it) block)

Calls the specified function block with this value as its argument and returns this value.

• block: A function to execute with the value. Must be synchronous: an async block compiles, but its Future is discarded and also returns before it completes.
• Returns: The original value.

R let<R>(R Function(T it) block)

Calls the specified function block with this value as its argument and returns its result.

• block: A function to execute with the value.
• Returns: The result of block.

Note: unlike Kotlin's ?.let, let does not short-circuit on null. On a nullable receiver the block is invoked with it == null. Use value?.let(...) to skip the block, or letWithElse to supply a fallback.

T? takeIf(bool Function(T it) predicate)

Returns this value if it satisfies the given predicate or null if it doesn't.

• predicate: A condition to evaluate.
• Returns: The value if it satisfies the condition, otherwise null.

T? takeUnless(bool Function(T it) predicate)

Returns this value if it does not satisfy the given predicate or null if it does.

• predicate: A condition to evaluate.
• Returns: The value if it does not satisfy the condition, otherwise null.

Extensions on Nullable Type [T?]

R letWithElse<R>(R Function(T it) block, {required R Function() orElse})

Calls the specified function block with this value as its argument and returns its result. If this is null, it invokes orElse and returns its result instead. orElse is only evaluated when this is null.

• block: A function to execute with the value if it's not null.
• orElse: A function producing the fallback value; only called if this is null.
• Returns: The result of block, or the result of orElse().

T withDefault(T defaultValue)

Returns this value if it's not null, otherwise returns the provided defaultValue. A method-chaining alternative to ??.

• defaultValue: A default value to return if this is null.
• Returns: The value or the default value.

Global Functions

R run<R>(R Function() block)

Calls the specified function block and returns its result.

• block: A function to execute.
• Returns: The result of block.