immutable method not callable using argument types () - doesn't make sense

[denizzzka]

On Tuesday, 27 March 2012 at 12:57:18 UTC, bearophile wrote:
> Steven Schveighoffer:
>
>> So what the compiler is saying is that you can't call dup with 
>> arguments (), you must call it with arguments '() immutable', 
>> meaning you must call it on an immutable B, not a mutable B.
>
> Any space for compiler error message improvements here?

+1, spent two hours with a similar problem