registerSingleton<T> method
registers a type as Singleton by passing an instance that will be returned on each call of get on that type
T
type to register
fun
factory funtion for this type
Implementation
void registerSingleton<T>(T instance) {
assert(allowReassignment || !_factories.containsKey(T),
"Type ${T.toString()} is already registered");
_factories[T] = new _ServiceFactory<T>(_ServiceFactoryType.constant,
instance: instance);
}