Dart と仲良くなる
kaito2If you’re sure that a variable is set before it’s used, but Dart disagrees, you can fix the error by marking the variable as late:
なるほど。
kaito2void main() {
late int lineCount = f();
print("=== Before eval ===");
print(lineCount);
print("=== After eval ===");
}
int f() {
print('f() is evaluated !!!');
return 777;
}
output
=== Before eval ===
f() is evaluated !!!
777
=== After eval ===
A final variable can be set only once; a const variable is a compile-time constant.
認識相違なし
Note: Instance variables can be final but not const.
ふむふむ
kaito2collection if か
kaito2
// Assign value to a
a = value;
// Assign value to b if b is null; otherwise, b stays the same
b ??= value;
kaito2
String playerName(String? name) => name ?? 'Guest';
kaito2
?[]
kaito2However, Dart programs can throw any non-null object—not just Exception and Error objects—as an exception.
どゆこと..？
kaito2late final とは？
kaito2
this を使うのは命名に被りがある場合のみ
kaito2コンストラクタを定義しなくても引数なしのデフォルトコンストラクタが利用できる
kaito2superclass のコンストラクタがようわからん
kaito2Initializer list あんまりわかってない
validation に使うっぽい
Point.withAssert(this.x, this.y) : assert(x >= 0) {
print('In Point.withAssert(): ($x, $y)');
}
kaito2Redirecting constructors なるほど
kaito2For example, a factory constructor might return an instance from a cache, or it might return an instance of a subtype. Another use case for factory constructors is initializing a final variable using logic that can’t be handled in the initializer list.
へー
kaito2factory ピンと来てない
kaito2
A common use case is ensuring that a type is non-nullable by making it a subtype of Object (instead of the default, Object?).
class Foo<T extends Object> {
// Any type provided to Foo for T must be non-nullable.
}
kaito2Lazily loading a library なるほど
kaito2await for
kaito2decimal/decimal