Move constexpr_first/last to common.h

This keeps it with constexpr_sum and the other metafunctions.

include/pybind11/cast.h

@@ -1314,25 +1314,6 @@ private:
     std::tuple<make_caster<Args>...> value;
 };
 
-NAMESPACE_BEGIN(constexpr_impl)
-/// Implementation details for constexpr functions
-constexpr int first(int i) { return i; }
-template <typename T, typename... Ts>
-constexpr int first(int i, T v, Ts... vs) { return v ? i : first(i + 1, vs...); }
-
-constexpr int last(int /*i*/, int result) { return result; }
-template <typename T, typename... Ts>
-constexpr int last(int i, int result, T v, Ts... vs) { return last(i + 1, v ? i : result, vs...); }
-NAMESPACE_END(constexpr_impl)
-
-/// Return the index of the first type in Ts which satisfies Predicate<T>
-template <template<typename> class Predicate, typename... Ts>
-constexpr int constexpr_first() { return constexpr_impl::first(0, Predicate<Ts>::value...); }
-
-/// Return the index of the last type in Ts which satisfies Predicate<T>
-template <template<typename> class Predicate, typename... Ts>
-constexpr int constexpr_last() { return constexpr_impl::last(0, -1, Predicate<Ts>::value...); }
-
 /// Helper class which collects only positional arguments for a Python function call.
 /// A fancier version below can collect any argument, but this one is optimal for simple calls.
 template <return_value_policy policy>

include/pybind11/common.h

@@ -449,6 +449,26 @@ constexpr size_t constexpr_sum() { return 0; }
 template <typename T, typename... Ts>
 constexpr size_t constexpr_sum(T n, Ts... ns) { return size_t{n} + constexpr_sum(ns...); }
 
+NAMESPACE_BEGIN(constexpr_impl)
+/// Implementation details for constexpr functions
+constexpr int first(int i) { return i; }
+template <typename T, typename... Ts>
+constexpr int first(int i, T v, Ts... vs) { return v ? i : first(i + 1, vs...); }
+
+constexpr int last(int /*i*/, int result) { return result; }
+template <typename T, typename... Ts>
+constexpr int last(int i, int result, T v, Ts... vs) { return last(i + 1, v ? i : result, vs...); }
+NAMESPACE_END(constexpr_impl)
+
+/// Return the index of the first type in Ts which satisfies Predicate<T>.  Returns sizeof...(Ts) if
+/// none match.
+template <template<typename> class Predicate, typename... Ts>
+constexpr int constexpr_first() { return constexpr_impl::first(0, Predicate<Ts>::value...); }
+
+/// Return the index of the last type in Ts which satisfies Predicate<T>, or -1 if none match.
+template <template<typename> class Predicate, typename... Ts>
+constexpr int constexpr_last() { return constexpr_impl::last(0, -1, Predicate<Ts>::value...); }
+
 // Extracts the first type from the template parameter pack matching the predicate, or Default if none match.
 template <template<class> class Predicate, class Default, class... Ts> struct first_of;
 template <template<class> class Predicate, class Default> struct first_of<Predicate, Default> {