How can I make a template resolve type only by first parameter?-CodePudding

How can I have a function like this

template<typename TValue>
TValue GridSnap(TValue Value, TValue Grid)

That resolves template type from only the first parameter like this

GridSnap(ADouble, AFloat)  => TValue should resolve to double
GridSnap(AFloat,  ADouble) => TValue should resolve to float
GridSnap(AFloat,  AInt)    => TValue should resolve to float

basically I don't want to manually cast the second argument, it would be nice if it could just do implicit cast base on the first parameter.

CodePudding user response：

What you want to do is to have the template parameter of the second function parameter to be in a non-deduced context. You can do this using std::type_identity like

template <typename TValue>
TValue GridSnap(TValue Value, std::type_identity_t<TValue> Grid)

If you can't use C 20, then you can just write your own type_identity and type_identity_t like

template <typename T>
struct type_identity 
{
    using type = T;
};

template <typename T>
using type_identity_t = typename type_identity<T>::type;

CodePudding user response：

@NathanOliver solution worked nicely, But I also found this solution

TValue GridSnapAuto(TValue Value, decltype(Value) Grid)