CODEWITHSUNDEEP
flutterdartextension-methodsnullability
Joel Broström
Joel Broström

Reputation: 4040

Is it possible to create a String extension `isEmptyOrNull` in dart?

First off let's define some criteria for this extension:

  1. It should return true if the object is null or an empty string.
  2. I should be able to use it on a chained nullable object.
  3. I should not have to use parentheses, type casts or == true when using the extension.

Here is an example that should work:

extension StringExtension on String? {
  bool get isEmptyOrNull {
  // Implementation
  }
}

class MyObject {
  MyObject({this.myString});

  final String? str;
}


// somewhere in the code: 

final MyObject? obj = null;
if(obj?.str.isEmptyOrNull){
  print('object was empty string or had the value null');
}

If this code compiles, follows all the criteria, and writes the correct output I would consider the solution correct.

Upvotes: 2

Views: 599

Answers (4)

mezoni
mezoni

Reputation: 11220

The operatot ?. is a conditional member access operator.

A conditional member access operator applies a member access (?.) operation to its operand only if that operand evaluates to non-null; otherwise, it returns null. That is:

If a evaluates to null, the result of a?.x is null.

If a evaluates to non-null, the result of a?.x is the same as the result of a.x.

This way your code will never be able to compile.

final MyObject? obj = null;
if(obj?.str.isEmptyOrNull){
  print('object was empty string or had the value null');
}

Upvotes: 1

Anton Nyström
Anton Nyström

Reputation: 11

How about this approach?

extension StringExtension on String? {
   bool get isEmptyOrNull => this?.isEmpty ?? true;
}

class MyObject {
   MyObject({this.myString});

   final String? str;
}

// somewhere in the code:

final MyObject? obj = null;
if (obj?.str.isEmptyOrNull) {
   print('Object was empty string or had the value null');
}

Upvotes: 1

Parrots Code
Parrots Code

Reputation: 31

Yes, it is possible to create a String extension isEmptyOrNull in Dart.

extension StringExtensions on String {
  bool get isNullOrEmpty => this == null || isEmpty;
}

To use the extension, you can simply call the isNullOrEmpty method on any string variable. For example:

String myString = '';

if (myString.isNullOrEmpty) {
  // The string is null or empty
} else {
  // The string is not null or empty
}

Upvotes: 1

Sayid
Sayid

Reputation: 443

I tried to write code according to all the criteria and it turned out like this

extension StringExtension on String? {
  bool get isNull => this == null;

  bool get isEmptyOrNull => isNull || this!.isEmpty;
}

class MyObject {
  MyObject({this.str});

  final String? str;
}

// somewhere in the code:

void main() {
  const MyObject? objNull = null;
  final MyObject objStrNull = MyObject();
  final MyObject objStrEmpty = MyObject(str: '');
  final MyObject objStrNotEmpty = MyObject(str: 'str');

  print(objNull?.str.isEmptyOrNull); // null
  print((objNull?.str).isEmptyOrNull); // true
  print(objStrNull.str.isEmptyOrNull); // true
  print(objStrEmpty.str.isEmptyOrNull); // true
  print(objStrNotEmpty.str.isEmptyOrNull); // false
}

But without parentheses with a null object it produces null and not boolean

Upvotes: 1

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