for_in_with_const_variable

A for-in loop variable can't be a 'const'.

The analyzer produces this diagnostic when the loop variable declared in a for-in loop is declared to be a const. The variable can't be a const because the value can't be computed at compile time.

The following code produces this diagnostic because the loop variable x is declared to be a const:

void f() {
  for (const x in [0, 1, 2]) {
    print(x);
  }
}

If there's a type annotation, then remove the const modifier from the declaration.

If there's no type, then replace the const modifier with final, var, or a type annotation:

void f() {
  for (final x in [0, 1, 2]) {
    print(x);
  }
}

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.