Compiler Explorer

Source code

#include <https://gist.githubusercontent.com/willkill07/428f248a7ff303ae672b0332ce419891/raw/a468d7c0684e999ddfdcc9eae6c073ddc0183a61/detector.hpp>
#include <https://gist.githubusercontent.com/willkill07/2b90a44828e280a0ade65b00b51dfa97/raw/f370b150a2d014bb6a18fe45122f6762765dd82c/concept_check.hpp>

template <class T>
using has_begin = decltype(std::declval<T>().begin());
template <class T>
using has_end = decltype(std::declval<T>().end());

template <typename T>
using HasBeginEnd = CheckConcept<
  And<
    Concept<has_begin, T>,
    Concept<has_end, T>>>;

template <typename T>
struct Base {
protected:
  T data;
  __host__ __device__ T* begin() {
    return &data;
  }
  __host__ __device__ T* end() {
    return &data;
  }
};

template <typename T>
class Derived : protected Base<T> {
public:
  using Base<T>::begin;
  using Base<T>::end;
};

struct Standalone {
  __host__ __device__ int* begin() {
    return nullptr;
  }
  __host__ __device__ int* end() {
    return nullptr;
  }
};

struct Simple {
protected:
  __host__ __device__ int* begin() {
    return nullptr;
  }
  __host__ __device__ int* end() {
    return nullptr;
  }
};

struct Complex : protected Simple {
public:
  using Simple::begin;
  using Simple::end;
};

struct VirtualBase {
  public:
  __host__ __device__ virtual int* begin() = 0;
  __host__ __device__ virtual int* end() = 0;
};

struct VirtualDerived : public VirtualBase {
  public:
  __host__ __device__ virtual int* begin() override {
    return nullptr;
  }
  __host__ __device__ virtual int* end() override {
    return nullptr;
  }
};

static_assert (HasBeginEnd<Standalone>::value,
  "Everything is fine");
  
static_assert (!HasBeginEnd<Base<int>>::value,
  "template protected base");
static_assert (!HasBeginEnd<Simple>::value,
  "non-template protected base");

static_assert (HasBeginEnd<Derived<int>>::value,
  "template derived from protected base");
static_assert (HasBeginEnd<Complex>::value,
  "non-template derived from protected base");

static_assert (HasBeginEnd<VirtualBase>::value,
  "virtual base");
static_assert (HasBeginEnd<VirtualDerived>::value,
  "virtual derived override");