non_bool_expression

The expression in an assert must be of type 'bool'.

The analyzer produces this diagnostic when the first expression in an assert has a type other than bool.

The following code produces this diagnostic because the type of p is int, but a bool is required:

void f(int p) {
  assert(p);
}

Change the expression so that it has the type bool:

void f(int p) {
  assert(p > 0);
}

Unless stated otherwise, the documentation on this site reflects Dart 3.8.0. Page last updated on 2025-05-08. View source or report an issue.