Null-aware operators in Dart

??=, ?? and ! — the rest of the null toolkit.

void main() {
  final counts = <String, int>{'wren': 3};

  // ??= assigns only when the current value is null.
  int? backupCameras;
  backupCameras ??= 1;
  print('Backups: $backupCameras');

  // Map lookups are nullable; chain the null-aware tools.
  final robins = counts['robin'] ?? 0;
  print('Robins so far: $robins');
  counts['robin'] = robins + 1;

  // ! asserts non-null and throws if you were wrong.
  final wrens = counts['wren']!;
  print('Wrens: $wrens');
}

How it works

1. ??= assigns only when the target is currently null.
2. counts['robin'] ?? 0 reads a missing key safely.
3. ! asserts non-null and throws if you were wrong — use it sparingly.

Keywords and builtins used here

• String
• final
• int
• void

The run, in numbers

Lines

17

Characters to type

450

Tokens

97

Three-star pace

70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 83 seconds.

Type this snippet

Step 2 of 3 in Null safety, step 17 of 27 in Language basics.

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