What can i do with a stored type? - dart

Question

Dart allows variables of types: Type type = SomeType; But for what purpose?
For example, foo bar baz are misapplications:
class A {
Type type = List;
foo() => new type();
type bar() {
return new List();
}
type baz = new List();
}
void main() {
Type type = String;
var str = "Hello Dart";
print(type == str.runtimeType);//true
print(str is String);//true
print(str is type); //type error.
}
I think this one is pretty neat:
void main() {
foo(Type t) {
switch (t){
case int: return 5;
case List: return [1,2,3]; // This one gets me every time :(
case String: return "Hello Dart!";
default: return "default";
}}
print(foo(10.runtimeType)); //5
print(foo([2,4,6].runtimeType)); //default
print(foo("lalala".runtimeType)); //Hello Dart!
print(foo(foo.runtimeType)); //default
}
Is its sole purpose to be the return type for methods like runtimeType and type matching ?

Answer 1

I don't think you can use it for generics. There you need type literals. But you can use it for reflection.
Just one simple example:
import 'dart:mirrors' as mirr;
class A {
String s;
A(this.s);
#override
String toString() => s;
}
void main() {
Type type = A;
var str = "Hello Dart";
mirr.ClassMirror cm = mirr.reflectType(type);
var s = cm.newInstance(new Symbol(''), [str]).reflectee;
print(s);
}
You could also create a Map with registered factories for different types to avoid the need for reflection.
(not tested)
class A {
String s;
int a = 0;
int b = 0;
int c = 0;
A(this.s);
A.extended(this.s, this.a, this.b, this.c);
#override
String toString() => '${super.toString()}: $s, $a, $b, $c';
}
void main(args) {
Type t = A;
registerType(t, (List args) => new A.extended(args[0], args[1], args[2], args[3]));
...
var a = getInstance(t, ['hallo', 1, 2, 3]);
}
Map<Type,Function> _factories = {};
void registerType(Type t, Function factory) {
_factories[t] = factory;
}
void getNewInstance(Type t, List args) {
return _factories[t](args);
}