constant_pattern_never_matches_value_type

The matched value type '{0}' can never be equal to this constant of type '{1}'.

The analyzer produces this diagnostic when a constant pattern can never match the value it's being tested against because the type of the constant is known to never match the type of the value.

The following code produces this diagnostic because the type of the constant pattern (true) is bool, and the type of the value being matched (x) is int, and a Boolean can never match an integer:

void f(int x) {
  if (x case true) {}
}

If the type of the value is correct, then rewrite the pattern to be compatible:

void f(int x) {
  if (x case 3) {}
}

If the type of the constant is correct, then rewrite the value to be compatible:

void f(bool x) {
  if (x case true) {}
}

Unless stated otherwise, the documentation on this site reflects Dart 3.8.1. Page last updated on 2025-05-08. View source or report an issue.