non_constant_map_pattern_key

Key expressions in map patterns must be constants.

The analyzer produces this diagnostic when a key in a map pattern isn't a constant expression.

The following code produces this diagnostic because the key A() isn't a constant:

void f(Object x) {
  if (x case {A(): 0}) {}
}

class A {
  const A();
}

Use a constant for the key:

void f(Object x) {
  if (x case {const A(): 0}) {}
}

class A {
  const A();
}

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.