How to tell if an object is an instance of a class

Question

How can I determine whether an object is of a class or not in the Dart language?

I'm looking to do something like the following:

if (someObject.class.toString() == "Num") {
    ...
}

And what is the returned value type? Will it have to be a String?

The mirror library has been up and down and seems to be subject to rapid change right now, as the one thing I did find simply did not work as shown.

score 53 · Answer 1 · edited Aug 15 '17 at 14:21

53

Recently Object got runtimeType getter. So, now we may not only compare type of object with another type, but actually get the class name of an object. As in:

myObject.runtimeType.toString()

Furthermore, in the current version of Dart, you can now skip toString operation and directly compare runtimeType of object with target type as in

myObject.runtimeType == int

or

myObject.runtimeType == Animal

edited Aug 15 '17 at 14:21

nbro

12,226
19
85
163

answered Oct 14 '12 at 10:42

Vadim Tsushko

1,448
9
10

1

One can compare directly using for instance `myObject.runtimeType == int`. – Daniel Nov 13 '14 at 11:22
1

Any advantages compared to `myObject is int`? `is` also returns true even when it only implements the other type this might not be the desired results in some cases. It was mentioned occasionally that `runtimeType` is not reliable because it can be overridden and should only be used for debugging purposes. – Günter Zöchbauer Nov 14 '14 at 07:55
1

I believe equality with runtimeType give you more dynamic capabilities. For example see that function: `testType(object,type) => object.runtimeType == type`. You can use it as `testType(myObject,int)` I believe it is impossible with `is` operator. But I should check it, maybe I wrong – Vadim Tsushko Nov 14 '14 at 09:31
2

I've checked, my guess was right. You cannot pass `type literal` as parameter of function and then use it in `is` operation. So `isOfType(obj, Type type) => obj is type` is incorrect but `isOfType(obj, Type type) => obj.runtimeType == type` works well – Vadim Tsushko Nov 15 '14 at 06:39
Better answer yet – Vidor Vistrom Nov 16 '18 at 16:38
2

If you use dart for web, minified to js code will return minified value! – Zufar Muhamadeev Dec 18 '18 at 07:43

score 43 · Accepted Answer · edited Jan 14 '19 at 05:21

43

By using the is and is! operators, like this:
```
if (someObject is T)
```
From the documentation:

The is and is! operators are handy for checking types. The result of obj is T is true if obj implements the interface specified by T. For example, obj is Object is always true.

Using the Mirrors API (see this example):

Expect.equals('T', someObject.simpleName)

edited Jan 14 '19 at 05:21

illright

3,586
2
24
43

answered Oct 14 '12 at 06:47

Eliran Malka

14,498
5
72
96

1

Thanks! Works beautifully. See quick test below: .... bool noteIsString(var note) { return( note is String ); } bool test0 = noteIsString("string"); bool test1 = noteIsString(123.45); print("test0 result is: $test0"); //=> true print("test1 result is: $test1"); //=> false – george koller Oct 14 '12 at 07:21

score 0 · Answer 3 · edited Oct 16 '20 at 05:14

0

Here is a simple explanation with a solution.

You have:

Object obj =t1;
where t1 is an object of class T.

And you have other object T called t.

T t = new T();

How to check if obj is the same type of t ?

Solution:

if(obj is t)
     print('obj is typeof t')
   else print('obj is not typeof t')

edited Oct 16 '20 at 05:14

David Buck

3,439
29
24
31

answered Oct 15 '20 at 20:37

Martinho Mussamba

51
5

How to tell if an object is an instance of a class

3 Answers3

Linked