dart中的Final和const很容易混淆，以至于我们认为它们是相同的。

让我们来看看它们的区别:

附注:我包括图像而不是文本，因为我不能将信息制成表格 在Stackoverflow .md格式轻松。

你不能使用final对象初始化const对象。例如:

  final myConst = 1;
  const myFinal = 2;

  final a = myConst; // possible
  final b = myFinal; // possible
  const c = myConst; // this is not possible
  const d = myFinal; // possible

dart中的Final和const很容易混淆，以至于我们认为它们是相同的。

让我们来看看它们的区别:

附注:我包括图像而不是文本，因为我不能将信息制成表格 在Stackoverflow .md格式轻松。

Const表示它的初始值必须是固定的，不能是动态值;

Final意味着它的初始值必须是固定的，但可以是一个动态值，等于具有固定值的var。

代码演示

常量

void main() {
  const sum = 1 + 2;
  // ✅ const can not change its value
  print("sum = ${sum}");
  // ⚠️ Const variables must be initialized with a constant value.
  const time = new DateTime.now();
  // ❌ Error: New expression is not a constant expression.
  print("time = ${time}");
}

最后

// new DateTime.now();
// dynamic timestamp

void main() {
  final sum = 1 + 2;
  // ✅ final can not change its value
  print("sum = ${sum}");
  final time = new DateTime.now();
  // ✅ final === var with fixed value
  print("time = ${time}");
}

截图

refs

https://dart.dev/guides/language/language-tour#final-and-const

如果你来自c++，那么Dart中的const在c++中是constexpr，而Dart中的final在c++中是const。

以上内容仅适用于基本类型。 然而在Dart中，标记为final的对象在其成员方面是可变的。

通过@Meyi扩展答案

final variable can only be set once and it is initialized when accessed.(for example from code section below if you use the value of biggestNumberOndice only then the value will be initialized and memory will be assigned). const is internally final in nature but the main difference is that its compile time constant which is initialized during compilation even if you don't use its value it will get initialized and will take space in memory. Variable from classes can be final but not constant and if you want a constant at class level make it static const.

代码:

void main() {

    // final demonstration
    final biggestNumberOndice = '6';
    //  biggestNumberOndice = '8';     // Throws an error for reinitialization

    // const
    const smallestNumberOnDice = 1;

}

class TestClass {

    final biggestNumberOndice = '6';

    //const smallestNumberOnDice = 1;  //Throws an error
    //Error .  only static fields can be declared as constants.

    static const smallestNumberOnDice = 1;
}