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prefer-moving-to-variable

added in: 1.6.0
warning
⚙️
Pro+

Warns when a property access or a method invocation start with duplicated chains of other invocations / accesses inside a single function or method block.

For instance, you have a function getUser() that returns a class instance with two fields: name and age. If you call this function twice inside another function body:

final name = getUser().name;
final age = getUser().age;

the rule will suggest to move getUser() call to a single variable.

⚙️ Config​

Set allowed-duplicated-chains (default is none) to configure a threshold after which the rule should trigger on duplicated lines (example).

Set ignored-invocations (default is empty) to configure a list of methods that should be excluded (example).

analysis_options.yaml
dart_code_metrics:
  rules:
    - prefer-moving-to-variable:
        allowed-duplicated-chains: 3
        ignored-invocations:
          - indexOf
          - someMethod

Example​

❌ Bad:

return Container(
  color: Theme.of(context).colorScheme.secondary, // LINT: Prefer moving repeated invocations to a variable and use it instead.
  child: Text(
    'Text with a background color',
    style: Theme.of(context).textTheme.headline6, // LINT: Prefer moving repeated invocations to a variable and use it instead.
  ),
);

✅ Good:

final theme = Theme.of(context);

return Container(
  color: theme.colorScheme.secondary, // Correct, replaced by a variable
  child: Text(
    'Text with a background color',
    style: theme.textTheme.headline6,
  ),
);

Example with "allowed-duplicated-chains"​

Config
analysis_options.yaml
dart_code_metrics:
  rules:
    - prefer-moving-to-variable:
        allowed-duplicated-chains: 3

✅ Good:

return Container(
  color: Theme.of(context).colorScheme.secondary, // Correct, repeated only 2 times
  child: Text(
    'Text with a background color',
    style: Theme.of(context).textTheme.headline6,
  ),
);

Example with "ignored-invocations"​

Config
analysis_options.yaml
dart_code_metrics:
  rules:
    - prefer-moving-to-variable:
        ignored-invocations:
          - of

✅ Good:

return Container(
  color: Theme.of(context).colorScheme.secondary, // Correct, 'of' is ignored
  child: Text(
    'Text with a background color',
    style: Theme.of(context).textTheme.headline6, // Correct, 'of' is ignored
  ),
);