CODEWITHSUNDEEP
c++template-meta-programming
pic11
pic11

Reputation: 14953

How to transform int parameter pack

Given a template

template <int... Ints>
struct FixedArray;

How to implement a meta function that multiplies each integer value by a given number?

template <int A, typename F>
struct Mul;

Mul<2, FixedArray<5, 7, 8>>::type

is the same as

FixedArray<10, 14, 16>

Upvotes: 1

Views: 224

Answers (1)

Ranoiaetep
Ranoiaetep

Reputation: 6647

To do this, you can first define an empty Mul class:

template<int A, typename T>
struct Mul;

Then create a specialization for FixedArray:

template<int A, int ... Ints>
struct Mul<A, FixedArray<Ints...>>
{
    using type = FixedArray<(Ints * A)...>;
};

However, I'd rather have a typedef inside FixedArray, so the resulting syntax looks more natural to me:

template <int ... Ints>
struct FixedArray
{
    template<int A>
    using Mul = FixedArray<(Ints * A)...>;
};

static_assert(std::same_as<FixedArray<1,2,3>::Mul<2>, FixedArray<2,4,6>>);

Upvotes: 3

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