test_enableIf.cpp

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#include "precompiled.hpp"
#include "memory/allStatic.hpp"
#include "metaprogramming/enableIf.hpp"
#include "utilities/debug.hpp"
#include <type_traits>
#include "unittest.hpp"

class EnableIfTest: AllStatic {
  class A: AllStatic {
  public:
    template <bool condition>
    static typename EnableIf<condition, char>::type test();
    template <bool condition>
    static typename EnableIf<!condition, long>::type test();
  };

  static const bool A_test_true_is_char = sizeof(A::test<true>()) == sizeof(char);
  STATIC_ASSERT(A_test_true_is_char);

  static const bool A_test_false_is_long = sizeof(A::test<false>()) == sizeof(long);
  STATIC_ASSERT(A_test_false_is_long);
};

template<typename T, ENABLE_IF(std::is_integral<T>::value)>
static T sub1(T x) { return x - 1; }

TEST(TestEnableIf, one_decl_and_def) {
  EXPECT_EQ(15, sub1(16));
}

template<typename T, ENABLE_IF(std::is_integral<T>::value)>
static T sub2(T x);

template<typename T, ENABLE_IF_SDEFN(std::is_integral<T>::value)>
T sub2(T x) { return x - 2; }

TEST(TestEnableIf, separate_decl_and_def) {
  EXPECT_EQ(14, sub2(16));
}

template<typename T>
struct TestEnableIfNested {
  template<typename U, ENABLE_IF(std::is_integral<U>::value)>
  static U sub1(U x);
};

template<typename T>
template<typename U, ENABLE_IF_SDEFN(std::is_integral<U>::value)>
U TestEnableIfNested<T>::sub1(U x) { return x - 1; }

TEST(TestEnableIf, nested_separate_decl_and_def) {
  EXPECT_EQ(15, TestEnableIfNested<void>::sub1(16));
}

// Demonstrate workaround for non-dependent condition.
template<typename T>
struct TestEnableIfNonDependent {
  // Dependent is used to make the ENABLE_IF condition dependent on
  // the type parameters for this function.
  template<typename Dependent = T, ENABLE_IF(std::is_same<int, Dependent>::value)>
  static T value() { return T{}; }
  static int instantiate() { return 5; }
};

TEST(TestEnableIf, non_dependent) {
  EXPECT_EQ(int{}, TestEnableIfNonDependent<int>::value());
  // This fails to compile if the ENABLE_IF for value() directly uses
  // T rather than indirectly via Dependent.
  EXPECT_EQ(5, TestEnableIfNonDependent<void>::instantiate());
}