avoid-casting-to-extension-type

v1.15.0

warning

recommended

dart 3.3+

has auto-fix

pro+

Warns when an expression is casted to an extension type.

Casting to an extension type can throw at runtime, whereas instantiating it is safe and you'll get a hint about the representation field type mismatch.

Example

❌ Bad:

void fn(String input) {
  // LINT: Avoid casting to extension type. Try instantiating it instead.
  final value1 = input as ET;
  
  // LINT: Avoid casting to extension type. Try instantiating it instead.
  final value2 = input as ET1;
}

extension type const ET(String s) {}
extension type const ET1(int v) {}

✅ Good:

void fn(String input) {
  final value = ET(input); // Correct, instantiated instead
}

extension type const ET(String s) {}

Additional Resources

• CWE-704: Incorrect Type Conversion or Cast

Related Rules

• avoid-implicitly-nullable-extension-types
• avoid-type-casts
• avoid-unrelated-type-casts
• avoid-unnecessary-type-casts