CODEWITHSUNDEEP
dart
Arrizal Shidiq
Arrizal Shidiq

Reputation: 83

dart : how to check generic type of property?

how to check the prop type when using it like this below

void main(){
  var obj = Ball<PassData>(data: PassData(id: 1,nama: 'asdas'));
  print('${obj.get()}');
}

class Ball<T>{
  T data;
  Ball({this.data});
  
  String get(){
    if(data is PassData){ //can't check it this way
      return 'this type has ${data.id} and ${data.nama}'; //compile error
    }
    else{
      return 'no : $data';
    }
  }
}

class PassData{
  String nama;
  int id;
  
  PassData({this.nama,this.id});
}

when using property of PassData object I've got an compile error like above. I need to get type of 'data' type property. Am I doing it wrong?

Upvotes: 0

Views: 1176

Answers (2)

Alperen Ekin
Alperen Ekin

Reputation: 318

Currently your data is in T type and your get class does not know which class it is belong to and therefore can not handle the operations. You can try this:

String get(){
if(this.data is PassData){ 
  return 'this type has ${(data as PassData).id} and ${(data as PassData).nama}'; 
}
else{
  return 'no : $data';
}

}

Upvotes: 0

lrn
lrn

Reputation: 71613

Your problem is not that the type is generic, but that the variable is not a local variable. Dart only promotes local variables, so doing if (data is PassData) doesn't promote the instance variable/field data to be a PassData.

Try writing it as:

  String get() {
    var data = this.data;
    if (data is PassData) {
      return 'this type has ${data.id} and ${data.nama}';
    } else {
      return 'no: $data';
    }
  }

Upvotes: 2

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