Dart Factory class for creating variables with type - flutter

Question

The problem is the following.
I had a typescript factory class that I attempted to do in Dart:
class FactoryClass{
factory FactoryClass(dynamic types, String className, dynamic defaultValue){
if(types[className] != null ){
return types[className](defaultValue);
}
else{
throw Exception("");
}
}
}
In TS it was used like this:
let variable= new FactoryClass([String, Number, etc...], "Number", "42")
That in TypeScript would give back a Number type variable with the value 42
However, it's not gonna work in Dart since types have no constructor for this. So I can't do something like
final myString = new String("def_value")
So the question arises, how can I go about it in dart?

Answer 1

You can do similar in Dart with just functions:
typedef Factory = dynamic Function(dynamic value);
dynamic create(Map<String, Factory> types, String className, dynamic defaultValue) {
if (types.containsKey(className)) {
return types[className]!(defaultValue);
} else {
throw Exception("no factory for $className");
}
}
final factories = <String, Factory>{
'String': (s) => s.toString(),
'int': (i) => i is int ? i : int.parse('$i'),
'bool': (b) => b is bool ? b : ('$b' == 'true'),
};
show(v) => print('Value $v has type ${v.runtimeType}');
main() {
show(create(factories, 'String', 'foo'));
show(create(factories, 'int', '42'));
show(create(factories, 'bool', 'false'));
}
Prints:
Value foo has type String
Value 42 has type int
Value false has type bool