concepts.hpp

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#pragma once
 
#include <concepts>
 
#define ein_ensures(concept, x) \
  ( \
    []<typename T> static constexpr noexcept { \
      static_assert(concept<T>, #concept " not satisfied"); \
    }.template operator()<decltype(x)>(), \
    (x) \
  )
 
#if defined(EIN_TESTING) || defined(EIN_TESTING_CONCEPTS)
#include <string>
 
// Sample functions using ein_ensures for test cases
static auto add_integers(std::integral auto x, std::integral auto y) {
  return ein_ensures(std::integral, x + y);
}
 
static auto add_floats(std::floating_point auto x, std::floating_point auto y) {
  return ein_ensures(std::floating_point, x + y);
}
 
template <typename T>
concept Stringifiable = requires(T a) {
  { std::to_string(a) } -> std::convertible_to<std::string>;
};
 
static auto stringifyable_addition(Stringifiable auto x, Stringifiable auto y) {
  return ein_ensures(Stringifiable, x + y);
}
 
TEST_CASE("concepts","[concepts]") {
  SECTION("Test integral addition with ein_ensures") {
    CHECK(add_integers(2, 3) == 5);
    CHECK(add_integers(-10, 4) == -6);
  }
 
  SECTION("Test floating-point addition with ein_ensures") {
    CHECK(add_floats(1.5, 2.0) == Catch::Approx(3.5));
    CHECK(add_floats(-10.0, 4.5) == Catch::Approx(-5.5));
  }
 
  SECTION("Test custom concept Stringifiable with ein_ensures") {
    CHECK(stringifyable_addition(10, 20) == 30);
  }
 
  SECTION("Test ein_ensures with non-matching concept should compile-time fail") {
      // Intentionally left commented as examples of cases that should fail to compile
      // REQUIRE(add_integers(2.5, 3.5) == 6.0); // Should fail on non-integral inputs
      // REQUIRE(add_floats(1, 2) == 3);         // Should fail on non-floating point inputs
  }
}
#endif