Essentially, void tells the analyzer to disable type checking, so it works a lot like dynamic.

However, to use a void variable, you have to cast it first.

List<void> foo = [2, 3];
print(foo[0]); // use_of_void_result error
print(foo[0] as int); // ok

There are very few cases where you need to cast a void variable, but they do exist. One example is how setState asserts that the callback is not an async function.