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avoid-unnecessary-patterns

v1.25.0
warning
dart 3.0+
configurable
pro+

Warns when a pattern variable declaration does not affect the type of an existing local variable.

Such declarations are often missing a type annotation or a null-check pattern.

⚙️ Config​

Set only-variables (default is true) to ignore patterns that are used a shorthand to a property access (example).

analysis_options.yaml
dart_code_metrics:
  rules:
    - avoid-unnecessary-patterns:
        only-variables: true

Example​

❌ Bad:

final value = 1;

void fn() {
  // LINT: Avoid unnecessary patterns.
  //  Try changing it to a different pattern, for example, the null-check pattern (?).
  if (value case final val) {}

  // LINT: Avoid unnecessary patterns.
  //  Try changing it to a different pattern, for example, the null-check pattern (?).
  if (value case var val) {}
}

✅ Good:

void fn() {
  if (value case final val?) {}
  if (value case final Object val) {}
  if (value.sign case final sign) {}
}

Example with "only-variables"​

Config
analysis_options.yaml
dart_code_metrics:
  rules:
    - avoid-unnecessary-patterns:
        only-variables: false

❌ Bad:

void fn() {
  // LINT: Avoid unnecessary patterns.
  //  Try changing it to a different pattern, for example, the null-check pattern (?).
  if (value.sign case final sign) {} // now also highlighted
}

Additional Resources​

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