tatsuyafujisaki / dart_playground

Personal playground for experimenting with new ideas in Dart

Lint

lint.md

Function

function.md

Asynchronous

asynchronous.md

Freezed

freezed.md

Riverpod

riverpod.md

CocoaPods

cocoa-pods.md

Test

test.md

Best practices

best-practices.md

Division, quotient, and remainder

print(10 / 3); // 3.33..
print(10 ~/ 3); // 3
print(10 % 3); // 1

Example of the ??= operator

void main() {
  String? a = 'a';
  String? b = null;

  a ??= 'c'; // 'c' will not be assigned to a because a is not null.
  b ??= 'c'; // 'c' will be assigned to b because b is null.

  print(a); // a
  print(b); // c
}

Required parameter / optional parameter / named parameter / unnamed (aka positional) parameter

Example of unnamed (aka positional) parameters

// a ia a required unnamed parameter.
// b is an optional unnamed (aka positional) parameter whose default value is null.
// c is an optional unnamed (aka positional) parameter with a default value.
class MyClass {
  MyClass(this.a, [this.b, this.c = 'default!']) {
    print('a = $a, b = $b, c = $c');
  }
  String a;
  String? b;
  String c;
}

void myFunction(
  String a, [
  String? b,
  String c = 'default!',
]) {
  print('a = $a, b = $b, c = $c');
}

void main() {
  MyClass('a');
  MyClass('a', 'b');
  MyClass('a', 'b', 'c');

  myFunction('a');
  myFunction('a', 'b');
  myFunction('a', 'b', 'c');
}

Example of named parameters

// a ia a required unnamed parameter.
// b ia a required named parameter.
// c is an optional named parameter whose default value is null.
// d is an optional named parameter with a default value.
class MyClass {
  MyClass(this.a, {required this.b, this.c, this.d = 'default!'}) {
    print('a = $a, b = $b, c = $c, d = $d');
  }
  String a;
  String b;
  String? c;
  String d;
}

void myFunction(
  String a, {
  required String b,
  String? c,
  String d = 'default!',
}) {
  print('a = $a, b = $b, c = $c, d = $d');
}

void main() {
  MyClass('a', b: 'b');
  MyClass('a', b: 'b', c: 'c');
  MyClass('a', b: 'b', c: 'c', d: 'd');

  myFunction('a', b: 'b');
  myFunction('a', b: 'b', c: 'c');
  myFunction('a', b: 'b', c: 'c', d: 'd');
}

How to convert List<dynamic> to List<String>

final xs = <dynamic>['a', 'b', 'c'];
print(xs.runtimeType); // List<dynamic>

final ys = List<String>.from(xs);
print(ys.runtimeType); // List<String>

// DON’T use cast() when a nearby operation will do
// https://dart.dev/effective-dart/usage#dont-use-cast-when-a-nearby-operation-will-do
// AVOID using cast()
// https://dart.dev/effective-dart/usage#avoid-using-cast
final zs = xs.cast<String>();
print(zs.runtimeType); // CastList<dynamic, String>