Written by Natig Babayev
on August 25, 2019

From Kotlin to Dart 2 Cheat Sheet - Basics

Print

Kotlin

println("Hello, World!")

Dart

print('Hello, World!');

Variables I

Kotlin

val x: Int = 0
val y = 1

Dart

final int x = 0;
final y = 1;

Variables II

Kotlin

var w: Int
var z = 2
z = 3
w = 1 

Dart

int w;
var z = 2;
z = 3;
w = 1;

Null I

Kotlin

var name: String? = null
println(name) // prints 'null'

name = "Natig"
println(name) // prints 'Natig'

val surname: String? = null
println(surname) // prints 'null'

Dart

String name; // by default, it's null
print(name); // prints 'null'

name = 'Natig';
print(name); // prints 'Natig'

final String surname = null; // final variable must be initialized
print(surname); // prints 'null'

Null II

Kotlin

var name: String? = null

val length = name?.length
println(length ?: 0) // prints '0'

name = name ?: "Undefined"
println(name) // prints 'Undefined'

Dart

String name; // by default, it is null

final length = name?.length;
print(length ?? 0); // prints '0'

name ??= 'Undefined';
print(name); // prints 'Undefined'

Strings I

Kotlin

val name = "Natig"
val surname = "Babayev"

val sentence = "I am $name $surname."
println(sentence) // prints 'I am Natig Babayev.'

val anotherSentence = "I am ${name.substring(0, 1)}. $surname."
println(anotherSentence) // prints 'I am N. Babayev.'

Dart

final name = 'Natig';
final surname = 'Babayev';

final sentence = 'I am $name $surname.';
print(sentence); // prints 'I am Natig Babayev.'

final anotherSentence = 'I am ${name.substring(0, 1)}. $surname.';
print(anotherSentence); // prints 'I am N. Babayev.'

Strings II

Kotlin

val text = """
First Line
Second Line
Third Line
"""

Dart

final multiLineString = '''
First Line
Second Line
Third Line
''';

Conditional expressions

Kotlin

val result = if (grade > 5) "grade > 5" else "grade <= 5"

Dart

final result = grade > 5 ? 'grade > 5' : 'grade <= 5';

As, Is

Kotlin

val a = 12

if (a is Int) {
    val result = a / 2
    println(result) // prints '6'
}

val length = (a as String).length
println(length) // throws exception

Dart

final a = 12;

if (a is int) {
  final result = a / 2;
  print(result); // prints '6'
}

final length = (a as String).length;
print(length); // throws exception

When / Switch

Kotlin

val a = .. // some value

val result = when (a) {
    in 0..2 -> "0..2"
    3, 4 -> "3 or 4"
    5 -> "it is 5"
    else -> "Unknown"
}

println(result)

Dart

final a = ..; // some value
var result;

switch (a) {
  case 0:
  case 1:
  case 2:
    result = '0..2';
    break;
  case 3:
  case 4:
    result = '3 or 4';
    break;
  case 5:
    result = 'it is 5';
    break;
  default:
    result = 'Unknown';
}

print(result);

For

Kotlin

for (i in 1 until 5) { }
for (i in 1..6 step 2) { }

for (item in collection) { }

Dart

for (var i = 1; i < 5; i++) { }
for (var i = 0; i <= 6; i += 2) { }

for (var item in collection) { }

Collections I

Kotlin

val numbers = listOf(17, 3, 1, 2)

val map = mapOf(1 to "One",
                2 to "Two",
                3 to "Three")

val mutableList = mutableListOf(1, 2, 3)

Dart

final numbers = List.unmodifiable([17, 3, 1, 2]);

final map = {
  1: 'One',
  2: 'Two',
  3: 'Three'
};

final mutableList = [1, 2, 3]

Collections II

Kotlin

val rangeOfNumbers = (0..12).toList()
val mutableRangeOfNumbers = (0..12).toMutableList()

Dart

final rangeOfNumbers = List.generate(13, (index) => index, growable: false);
final mutableRangeOfNumbers = List.generate(13, (index) => index);

Collections III

Kotlin

numbers.forEach(::println)

numbers.filter { it > 5 }
    .forEach { value -> println(value) }

Dart

numbers.forEach(print);

numbers.where((it) => it > 5).forEach((value) => print(value));

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