invalid_exception_value

The method {0} can't have an exceptional return value (the second argument) when the return type of the function is either 'void', 'Handle' or 'Pointer'.

The analyzer produces this diagnostic when an invocation of the method Pointer.fromFunction or NativeCallable.isolateLocal has a second argument (the exceptional return value) and the type to be returned from the invocation is either void, Handle or Pointer.

For more information about FFI, see C interop using dart:ffi.

The following code produces this diagnostic because a second argument is provided when the return type of f is void:

import 'dart:ffi';

typedef T = Void Function(Int8);

void f(int i) {}

void g() {
  Pointer.fromFunction<T>(f, 42);
}

Remove the exception value:

import 'dart:ffi';

typedef T = Void Function(Int8);

void f(int i) {}

void g() {
  Pointer.fromFunction<T>(f);
}

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.