How do i check a type against its parent class?

Question

Simple cases of, int being a number really.

Im creating a generic class test<T>

and i want to test T to see if its inherited from number (or num in the case of Dart).

Based on the Objects, Object > num > int in the docs, so at first I was thinking that: T is num would work if T is int. Testing int is num shows false. There must be another keyword i need to use instead of is to determine if it is a child of a particular class.

Im trying to set it up such that if T is a child of num it will process comparisons differently than if they were strings.

To me, this goes back to the polymorphism-inheritance design of is-a and has-a relationshis.

Answer 1

1. The Answer

With int is num you test if an instance of Type is a subtype of num which is correctly reported as false.

What you want to test is rather like 5 is num.

Try it in DartPad.

2. Additional, Useful Info

As noted in the comments, it's also useful to note that is tests for the runtime type. So, if you're working with a non-initialized variable — e.g., int nonInitializedVar; —, with runtime type of Null, Dart will return false to the is test, because Null is not a subclass of num.

Another important point is that if you want to use is on types (classes) at runtime you will need to use reflection, with packages such as dart:mirrors or reflectable or the dart-analyzer to do it at build time for code generation.