default_value_in_function_type

Parameters in a function type can't have default values.

The analyzer produces this diagnostic when a function type associated with a parameter includes optional parameters that have a default value. This isn't allowed because the default values of parameters aren't part of the function's type, and therefore including them doesn't provide any value.

The following code produces this diagnostic because the parameter p has a default value even though it's part of the type of the parameter g:

void f(void Function([int p = 0]) g) {
}

Remove the default value from the function-type's parameter:

void f(void Function([int p]) g) {
}

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.