To reproduce.

function main() {
    let v: f64 =  1u64 as! f64
    println("{}", v)
}

Error message:

build/Test-Generic-Return-Float-issue-1071.cpp:5:16: error: no matching function for call to 'verify_cast'
const f64 v = (verify_cast<f64>((static_cast<u64>(1ULL))));
               ^~~~~~~~~~~~~~~~
runtime/Jakt/TypeCasts.h:47:49: note: candidate function [with OutputType = double, InputType = unsigned long] not viable: expects an l-value for 1st argument
ALWAYS_INLINE CopyConst<InputType, OutputType>& verify_cast(InputType& input)
                                                ^
runtime/Jakt/TypeCasts.h:39:49: note: candidate template ignored: could not match 'InputType *' against 'u64' (aka 'unsigned long')
ALWAYS_INLINE CopyConst<InputType, OutputType>* verify_cast(InputType* input)