如何覆盖 Dart/flutter 上的变量

Question

I'm coming from TS/JS background and I was overriding properties using it previous value with something like this in Javasctipt/Typesctipt :

let arr = ['messi', 'mo salah'];
arr = arr.filter( name => name != 'messi');

// results
// arr = ['mo salah'];

Now in Dart , I can't do that and I have searched through the docs/internet and didn't find useful answers for the right syntax!

What I did is same as above code:

var arr = ['messi', 'mo salah'];
arr = arr.where( (name) => name != 'messi' );

// results
nothing showing up

I have seen on some articles for creating a search with the dart that they clearing the arr first then adding the new filter arr:

var arr = ['messi', 'mo salah'];
var filter = arr.where( (name) => name != 'messi' );

// then
arr.clear();
arr.addAll(filter);

Answer 1

You can use retainWhere , result: [no salah]

List<String> x = ["messi", "no salah"];
x.retainWhere((f) => f != "messi");
print(x);

Your code will create a new list, but this code will update your list. You can choose which is useful for your purpose.

Answer 2

The problem is where method on lists returns a variable with type WhereIterable<String> . You can see it by running the following code:

 void main() {
   dynamic arr = ['messi', 'mo salah'];
   arr = arr.where((name) => name != 'messi');
   print(arr.runtimeType); // WhereIterable<String>
 }

When you wrote var arr List became the type and as Dart is a strictly-typed language, you can't assign a value of type x to a variable of type y , unless one of them is dynamic. The dynamic type means that it can take any type, like any in TS. So you have to call toList() on arr to convert it from iterable to a list:

 void main() {
   var arr = ['messi', 'mo salah'];
   arr = arr.where((name) => name != 'messi').toList();
   print(arr); // [mo salah]
 }

Answer 3

I have found the answer to my question while I'm writing it here,

what I was missing? is or the difference between filter in TS/JS and where in dart that filter return array type but where is not and I have to convert it to an array by adding toList() at the end.

So my final code in dart should look like this:

var arr = ['messi', 'mo salah'];
arr = arr.where( (name) => name != 'messi' ).toList();

// results
// arr = ['mo salah'];