core: Add crtp helper class.

core/CMakeLists.txt

@@ -6,6 +6,7 @@ add_headers(core GAP_CORE_HEADERS
 	concepts.hpp
 	config.hpp
 	coroutine.hpp
+	crtp.hpp
 	dense_map.hpp
 	generator.hpp
 	hash.hpp

core/include/gap/core/crtp.hpp

@@ -0,0 +1,20 @@
+// Copyright (c) 2024, Trail of Bits, Inc.
+
+#pragma once
+
+namespace gap::core {
+
+    template< typename T, template< typename > class crtp_type >
+    struct crtp
+    {
+        T &underlying() { return static_cast< T & >(*this); }
+
+        const T &underlying() const { return static_cast< const T & >(*this); }
+
+      private:
+        crtp() {}
+
+        friend crtp_type< T >;
+    };
+
+} // namespace gap::core

test/core/CMakeLists.txt

@@ -3,6 +3,7 @@
 add_gap_test(test-gap-core
     bigint.cpp
     benchmark.cpp
+    crtp.cpp
     dense_map.cpp
     hash.cpp
     memoize.cpp

test/core/crtp.cpp

@@ -0,0 +1,25 @@
+// Copyright (c) 2022-present, Trail of Bits, Inc.
+
+#include <array>
+#include <doctest/doctest.h>
+#include <gap/core/crtp.hpp>
+
+namespace gap::test
+{
+    template< typename derived >
+    struct base : gap::core::crtp< derived, base > {
+        using gap::core::crtp< derived, base >::underlying;
+
+        int foo() { return underlying().bar(); }
+    };
+
+    struct derived : base< derived > {
+        int bar() { return 10; }
+    };
+
+    TEST_CASE("CRTP test") {
+        derived d;
+        CHECK(d.foo() == 10);
+    }
+
+} // namespace gap::test