To reproduce:

function f<T>(anon n: u64) -> T {
    let v: T = n as! T

    return v
}

function main() {
    let value: f64 =  f<f64>(1u64)
    println("{}", value)
}

Error message:

runtime/Jakt/TypeCasts.h:23:12: error: 'double' is not a class type
    return dynamic_cast<CopyConst<InputType, OutputType>*>(&input);
           ^           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
runtime/Jakt/TypeCasts.h:50:12: note: in instantiation of function template specialization 'Jakt::is<double, const unsigned long>' requested here
    VERIFY(is<OutputType>(input));
           ^
runtime/Jakt/Assertions.h:13:20: note: expanded from macro 'VERIFY'
#    define VERIFY assert
                   ^
build/Test-Generic-Return-Float.cpp:9:14: note: in instantiation of function template specialization 'Jakt::verify_cast<double, const unsigned long>' requested here
const T v = (verify_cast<T>((n)));
             ^
build/Test-Generic-Return-Float.cpp:16:19: note: in instantiation of function template specialization 'Jakt::f<double>' requested here
const f64 value = f<f64>(static_cast<u64>(1ULL));