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avoid-duplicate-map-keys

added in: 1.13.0
warning
🛠
Pro+
preset: recommended

Warns when a map has duplicate keys.

Using duplicate keys in the same map declaration is undesirable, since each such key will override the previous value.

Example​

❌ Bad:

void fn() {
  final map = {
    'key': 'value',
    'key': 'value', // LINT: Avoid duplicate keys in maps. Try removing or changing the key.
    ...{'key': 'value'}, // LINT: Avoid duplicate keys in maps. Try removing or changing the key.
    if (...) 'key': 'value', // LINT: Avoid duplicate keys in maps. Try removing or changing the key.
  };

  final override = {
    if (...) 'key': 'value',
    'key': 'value', // LINT: This entry unconditionally overrides the previous entry with the same key. Try changing the key or removing the entry inside an if element.
  };
}

✅ Good:

void fn() {
  final map = { // Correct, no duplicate keys
    'key': 'value',
    'anotherKey': 'value',
    ...{'thirdKey': 'anotherValue'},
  };

  final override = {
    'key': 'value', // Correct, no duplicate keys
  };
}

Additional Resources​