How to make a Currency class from std.BigInt?

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The next version https://bpaste.net/show/dc3c5f10f2ca
I use https://github.com/dsimcha/Rational/blob/master/rational.d
I want to do it:
auto c = new Currencies!Rational.rational.Rational!(BigInt);
where Rational.rational.Rational it is std.rational.Rational
I get the error:
Error: template instance Currencies!(Rational) does not match 
template declaration Currencies(T)