Error when returning `Windows.Foundation.Numerics.Rational`

[jaigak]

When returning a WinRT structure from a method on a runtime class, I seem to get this error:

error C2679: binary '=': no operator found which takes a right-hand operand of type 'winrt::impl::struct_Windows_Foundation_Numerics_Rational' (or there is no acceptable conversion) (compiling source file Numerics.cpp)
message : could be 'winrt::Windows::Foundation::Numerics::Rational &winrt::Windows::Foundation::Numerics::Rational::operator =(winrt::Windows::Foundation::Numerics::Rational &&)' (compiling source file Numerics.cpp)
message : or 'winrt::Windows::Foundation::Numerics::Rational &winrt::Windows::Foundation::Numerics::Rational::operator =(const winrt::Windows::Foundation::Numerics::Rational &)' (compiling source file Numerics.cpp)
message : while trying to match the argument list '(winrt::Windows::Foundation::Numerics::Rational, winrt::impl::struct_Windows_Foundation_Numerics_Rational)' (compiling source file Numerics.cpp)

[kennykerr]

Unfortunately someone added Rational without informing language projections, so it didn’t get the same special treatment as other numerics, and now it needs its own special handling. Fixed with #1106

[jaigak]

Would like to see operators for Rational just like other Numerics types so it's more useful out of the box. I currently have this in my code, doesn't bother with simplifying although the inputs themselves have no requirement on that and can simplify manually if needed.

constexpr Rational operator+(Rational const& left, Rational const& right) noexcept
{
    auto const newDenominator = left.Denominator * right.Denominator;
    auto const newNumerator = left.Numerator * right.Denominator + right.Numerator * left.Denominator;
    return { newNumerator, newDenominator };
}

constexpr Rational operator-(Rational const& left, Rational const& right) noexcept
{
    auto const newDenominator = left.Denominator * right.Denominator;
    auto const newNumerator = left.Numerator * right.Denominator - right.Numerator * left.Denominator;
    return { newNumerator, newDenominator };
}

constexpr Rational operator*(Rational const& left, Rational const& right) noexcept
{
    auto const newNumerator = left.Numerator * right.Numerator;
    auto const newDenominator = right.Denominator * right.Denominator;
    return { newNumerator, newDenominator };
}

constexpr Rational operator/(Rational const& left, Rational const& right) noexcept
{
    auto const newNumerator = left.Numerator * right.Denominator;
    auto const newDenominator = left.Denominator * right.Numerator;
    return { newNumerator, newDenominator };
}