deduce

Extension for working well with CTAD.
bemanproject · Feb 1, 2025 · 73732e0 · 73732e0
1 parent 0e1a55e
commit 73732e0
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diff --git a/include/beman/elide/deduce.hpp b/include/beman/elide/deduce.hpp
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#ifndef BEMAN_ELIDE_DEDUCE_HPP
+#define BEMAN_ELIDE_DEDUCE_HPP
+
+#include <type_traits>
+#include <beman/elide/elide.hpp>
+
+namespace beman::elide {
+
+namespace detail::deduce {
+
+template<typename>
+struct is_elide : std::false_type {};
+template<typename T, typename... Args>
+struct is_elide<beman::elide::elide<T, Args...>> : std::true_type {};
+
+}
+
+template<typename T>
+struct deduce : std::remove_cvref<T> {};
+template<typename T>
+  requires
+    detail::deduce::is_elide<
+      std::remove_cvref_t<T>>::value &&
+    std::is_invocable_v<T>
+struct deduce<T> : std::invoke_result<T> {};
+
+template<typename T>
+using deduce_t = typename deduce<T>::type;
+
+} // namespace beman::elide
+
+#endif // BEMAN_ELIDE_DEDUCE_HPP
diff --git a/src/beman/elide/CMakeLists.txt b/src/beman/elide/CMakeLists.txt
@@ -8,7 +8,9 @@ target_sources(
     PUBLIC
         FILE_SET HEADERS
         BASE_DIRS ${PROJECT_SOURCE_DIR}/include
-        FILES ${PROJECT_SOURCE_DIR}/include/beman/elide/elide.hpp
+        FILES
+            ${PROJECT_SOURCE_DIR}/include/beman/elide/deduce.hpp
+            ${PROJECT_SOURCE_DIR}/include/beman/elide/elide.hpp
 )
 
 set_target_properties(beman.elide PROPERTIES VERIFY_INTERFACE_HEADER_SETS ON)

diff --git a/tests/beman/elide/CMakeLists.txt b/tests/beman/elide/CMakeLists.txt
@@ -10,3 +10,12 @@ target_link_libraries(
 )
 
 gtest_add_tests(beman.elide.tests.elide "" AUTO)
+
+add_executable(beman.elide.tests.deduce)
+target_sources(beman.elide.tests.deduce PRIVATE deduce.test.cpp)
+target_link_libraries(
+    beman.elide.tests.deduce
+    PRIVATE beman::elide GTest::gtest GTest::gtest_main
+)
+
+gtest_add_tests(beman.elide.tests.deduce "" AUTO)
diff --git a/tests/beman/elide/deduce.test.cpp b/tests/beman/elide/deduce.test.cpp
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <beman/elide/deduce.hpp>
+
+#include <type_traits>
+#include <utility>
+#include <beman/elide/elide.hpp>
+
+#include <gtest/gtest.h>
+
+namespace beman::elide {
+
+namespace {
+
+struct factory {
+  int operator()();
+};
+
+struct no_lvalue_factory {
+  int operator()() &&;
+};
+
+struct split_factory {
+  int operator()() &;
+  double operator()() &&;
+};
+
+template<typename T>
+struct wrapper {
+  template<typename U>
+  explicit wrapper(U&& u) noexcept(
+    std::is_nothrow_constructible_v<T, U>)
+    : t_(std::forward<U>(u))
+  {}
+  constexpr const T& get() const noexcept {
+    return t_;
+  }
+private:
+  T t_;
+};
+
+template<typename T>
+explicit wrapper(T&&) -> wrapper<deduce_t<T>>;
+
+}
+
+static_assert(!detail::deduce::is_elide<int>::value);
+static_assert(detail::deduce::is_elide<elide<factory&>>::value);
+
+static_assert(std::is_same_v<int, deduce_t<int>>);
+static_assert(std::is_same_v<int, deduce_t<int&>>);
+static_assert(std::is_same_v<int, deduce_t<const int&>>);
+static_assert(std::is_same_v<int, deduce_t<int&&>>);
+static_assert(std::is_same_v<int, deduce_t<const int&&>>);
+
+static_assert(
+  std::is_same_v<
+    int,
+    deduce_t<
+      elide<factory&>>>);
+static_assert(
+  std::is_same_v<
+    int,
+    deduce_t<
+      elide<factory&>&>>);
+static_assert(
+  std::is_same_v<
+    int,
+    deduce_t<
+      const elide<factory&>&>>);
+static_assert(
+  std::is_same_v<
+    int,
+    deduce_t<
+      elide<factory&>&&>>);
+static_assert(
+  std::is_same_v<
+    int,
+    deduce_t<
+      const elide<factory&>&&>>);
+
+static_assert(
+  std::is_same_v<
+    int,
+    deduce_t<
+      elide<no_lvalue_factory&&>>>);
+static_assert(
+  std::is_same_v<
+    int,
+    deduce_t<
+      elide<no_lvalue_factory&&>&&>>);
+static_assert(
+  std::is_same_v<
+    int,
+    deduce_t<
+      const elide<no_lvalue_factory&&>&&>>);
+static_assert(
+  std::is_same_v<
+    elide<no_lvalue_factory&&>,
+    deduce_t<
+      const elide<no_lvalue_factory&&>&>>);
+static_assert(
+  std::is_same_v<
+    elide<no_lvalue_factory&&>,
+    deduce_t<
+      elide<no_lvalue_factory&&>&>>);
+
+static_assert(
+  std::is_same_v<
+    double,
+    deduce_t<
+      elide<split_factory&&>>>);
+static_assert(
+  std::is_same_v<
+    double,
+    deduce_t<
+      elide<split_factory&&>&&>>);
+static_assert(
+  std::is_same_v<
+    int,
+    std::invoke_result_t<
+      elide<split_factory&&>&>>);
+static_assert(
+  std::is_same_v<
+    int,
+    deduce_t<
+      elide<split_factory&&>&>>);
+
+TEST(Deduce, basic) {
+  wrapper w(elide([]() noexcept { return 5; }));
+  EXPECT_EQ(5, w.get());
+}
+
+}