CODEWITHSUNDEEP
dart
Woton Sampaio
Woton Sampaio

Reputation: 456

How check type reference - dart

If I have a object like this:

class MyClass<K>{...

How I could check type of K? If was a variable was easy, ex:

(myVar is Object)... //true | false

But in my case, this dont works:

(K is Object) // awalys false

Upvotes: 0

Views: 146

Answers (2)

Christopher Moore
Christopher Moore

Reputation: 17113

You want == here. Using is is for comparing the type of variable, not a literal type.

This will only check if K is actually Object if you use K == Object. If you pass K as int for instance, it will not be considered to be an Object.

Upvotes: 1

lrn
lrn

Reputation: 71603

I recommend not using == for comparison of Type objects. It only checks exact equality, which might be useful in a few situations, but in plenty of situations you do want a subtype check.

You can get that subtype check using a helper function like:

bool isSubtype<S, T>() => <S>[] is List<T>;

Then you can check either isSubtype<K, Object> to check if K is a subtype of Object (which is true for everything except Null and types equivalent to Object?, but that can also be checked like null is! K), or isSubtype<Object, K> to check whether K is a supertype of Object.

It has the advantage that you can compare to any type, not just types you can write literals for. For example K == List only works for List<dynamic>. If you need to check whether K is a List<int>, you can do isSubtype<K, List<int>>.

You can get equivalence of types (mutual subtype), without requiring them to be the same type, by doing isSubtype in both directions. For example isSubtype<Object?, dynamic>() and isSubtype<dynamic, Object?>() are both true, but if K is Object? then K == dynamic is false.

Upvotes: 0

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