Default values of an optional parameter must be constant

Question

I've been trying to get this right for some time and can't figure out what is wrong.

enum MyEnum { a, b }  class ClassA {   final MyEnum myEnum;   ClassA({this.myEnum = MyEnum.a}); }  class ClassB {   final ClassA classA;   ClassB({this.classA = ClassA()}); // ClassA expression is underlined with red } 

The IDE (Visual Studio Code) complains with:

[dart] Default values 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. Can anyone see what I am doing wrong here?

Answer 1

Try

enum MyEnum { a, b }  class ClassA {   final MyEnum myEnum;   ClassA({this.myEnum}); }  class ClassB {   final ClassA classA;   ClassB({this.classA}); // ClassA expression is underlined with red } 

no need for '=' operator. It will automatically assign the value when you will pass it to the constructor.

Use the '=' operator only when you need to pass a default value to your variables hence, making them optional parameters.

Edit

enum MyEnum { a, b }  class ClassA {   final MyEnum myEnum;   const ClassA({this.myEnum = MyEnum.a}); }  class ClassB {   final ClassA classA;   ClassB({this.classA = const classA()}); // ClassA expression is underlined with red } 

This is the only way i could find to achieve what you want, the constructor should be default

This is called a canonicalized constructor.