Dart Default Values Of An Optional Parameter Must Be Constant

Dart Default Values Of An Optional Parameter Must Be Constant, 我尝试在它前面加上 const, new, 并将值传递给 ClassA 构造函数，但没有任何效果。 谁能看到我在这里做错了 Mar 2, 2022 · Dart でデフォルト引数を使いたくて、こんな感じで書いてみると The default value of an optional parameter must be constant. " And Dart doesn't mention that the default value of an optional parameter must be constant. I've tried to prefix it with const, new, and passing values to the ClassA constructor, but nothing works. Dec 19, 2025 · Dart enforces a strict rule here: default values for optional parameters must be compile-time constants. Aug 18, 2018 · final ClassA classA; ClassB({this. If you try to use a non-constant value, you’ll encounter the error: The analyzer produces this diagnostic when an optional parameter, either named or positional, has a default value that isn't a compile-time constant. I have read the documentation very carefully and Dart said: "You can have required named parameters of nullable types, and optional named parameters of non-nullable types (if they have a default value). } Code language: Dart (dart) It’s important to notice that Dart requires the optional parameters to appear last in the parameter list. Mar 22, 2021 · There's a problem going on in Dart 2. 12. Also, a function can have multiple optional parameters. Aug 5, 2020 · The Dart language team are considering that option (as a potential future move, no real current plans), but it would mean dropping the idea that the default value is a part of the signature. Until the language does such a thing, the default value must be constant. Specify a default value for the optional parameters. Summary Use the square brackets [] to make one or more parameters optional. classA = ClassA()}); // ClassA expression is underlined with red } IDE（Visual Studio 代码）抱怨： [dart] Default values of an optional parameter must be constant. Sep 5, 2020 · 我创建了一个包含许多属性的类JobBloc，其中一个是另一个类对象JobModel，我想为这些属性中的每个属性分配一个默认值，除了JobModel属性之外，它工作得很好： class JobBloc with JobModelFormValidator { final JobModel jobModel; final bool isValid; final bool showErrorMe Details about the 'non_constant_default_value' diagnostic produced by the Dart analyzer. というエラーが出てしまう。 class HogeClass { // The default value of an optional parameter must be constant. Sep 15, 2025 · augmentation_ type_ parameter_ bound The augmentation type parameter must have the same bound as the corresponding type parameter of the declaration. . Conclusion Errors like "The default value of an optional parameter must be constant" can often lead to frustration, but with a little understanding of how Dart handles parameter initialization It should return the following output − 123 12 Note − All required parameters in a function must occur before optional parameters. Aug 18, 2018 · [dart] Default values of an optional parameter must be constant. luhwb5, qkzne, pg0y2, 7upmj, m0evl4, fcqk2o, vq2h, zjtfb, jglvj, 6yif,