From d3cb6f324f5bcafd2716764d935268ee0d40a348 Mon Sep 17 00:00:00 2001
From: Tobias Zindl <zie.develop@gmail.com>
Date: Fri, 13 Oct 2023 18:59:51 +0200
Subject: [PATCH] :sparkles: add first function_ref implementation

* the current implementation only supports up to one argument
* void return type is currently not fully supported
---
 ...3-10-13T17_05_55Z_post_HJOtakocHZZVtTha.md |   8 +
 .../functional/detail/bound_entity_type.hpp   |  53 ++++++
 include/zll/functional/detail/fn_types.hpp    |  18 +++
 include/zll/functional/function_ref.hpp       | 153 ++++++++++++++++++
 .../functional/function_ref_tests.cpp         | 112 +++++++++++++
 tests/unit_tests/meson.build                  |   2 +
 6 files changed, 346 insertions(+)
 create mode 100644 docs/sherds/2023/2023-10/2023-10-13T17_05_55Z_post_HJOtakocHZZVtTha.md
 create mode 100644 include/zll/functional/detail/bound_entity_type.hpp
 create mode 100644 include/zll/functional/detail/fn_types.hpp
 create mode 100644 include/zll/functional/function_ref.hpp
 create mode 100644 tests/unit_tests/functional/function_ref_tests.cpp

diff --git a/docs/sherds/2023/2023-10/2023-10-13T17_05_55Z_post_HJOtakocHZZVtTha.md b/docs/sherds/2023/2023-10/2023-10-13T17_05_55Z_post_HJOtakocHZZVtTha.md
new file mode 100644
index 0000000..bbb51cb
--- /dev/null
+++ b/docs/sherds/2023/2023-10/2023-10-13T17_05_55Z_post_HJOtakocHZZVtTha.md
@@ -0,0 +1,8 @@
+Shortcuts for `function_ref`
+
+We made some shortcuts in the `function_ref` implementation:
+
+* direct call to the callables (no `invoke`), this could mess up the calls for binding
+* no specialisation to `invocables` this could end up in ugly compiler errors
+* only support for one argument (to much boilerplate)
+* void is not proper supported (would need a specialisation)
diff --git a/include/zll/functional/detail/bound_entity_type.hpp b/include/zll/functional/detail/bound_entity_type.hpp
new file mode 100644
index 0000000..4f9959f
--- /dev/null
+++ b/include/zll/functional/detail/bound_entity_type.hpp
@@ -0,0 +1,53 @@
+#ifndef ZLL_FUNCTIONAL_DETAIL_BOUNDENTITYTPE_HPP
+#define ZLL_FUNCTIONAL_DETAIL_BOUNDENTITYTPE_HPP
+
+#include "zll/meta/traits/enable_if.hpp"
+#include "zll/meta/traits/is_const.hpp"
+#include "zll/meta/traits/is_function.hpp"
+#include "zll/meta/traits/is_object.hpp"
+
+namespace zll {
+namespace detail {
+
+struct bound_entity_object {};
+struct bound_entity_function {};
+
+union bound_entity_type {
+    void* object_ptr;
+    const void* const_object_ptr;
+    void (*fn_ptr)();
+
+    bound_entity_type() : object_ptr(NULL) {}
+
+    template <typename T>
+    explicit bound_entity_type(T* ptr, bound_entity_object) : object_ptr(ptr) {}
+
+    template <typename T>
+    explicit bound_entity_type(const T* ptr, bound_entity_object) : const_object_ptr(ptr) {}
+
+    template <typename T>
+    explicit bound_entity_type(T* ptr, bound_entity_function) : fn_ptr(reinterpret_cast<void (*)()>(ptr)) {}
+};
+
+template <typename T>
+static typename zll::meta::enable_if<zll::meta::is_object<T>::value && zll::meta::is_const<T>::value, T*>::type get(
+    bound_entity_type entity) {
+    return static_cast<T*>(entity.const_object_ptr);
+}
+
+template <typename T>
+static typename zll::meta::enable_if<zll::meta::is_object<T>::value && !(zll::meta::is_const<T>::value), T*>::type get(
+    bound_entity_type entity) {
+    return static_cast<T*>(entity.object_ptr);
+}
+
+template <typename T>
+static typename zll::meta::enable_if<!zll::meta::is_object<T>::value && (zll::meta::is_function<T>::value), T*>::type
+get(bound_entity_type entity) {
+    return reinterpret_cast<T*>(entity.fn_ptr);
+}
+
+}  // namespace detail
+}  // namespace zll
+
+#endif  // ZLL_FUNCTIONAL_DETAIL_BOUNDENTITYTPE_HPP
diff --git a/include/zll/functional/detail/fn_types.hpp b/include/zll/functional/detail/fn_types.hpp
new file mode 100644
index 0000000..58bf03e
--- /dev/null
+++ b/include/zll/functional/detail/fn_types.hpp
@@ -0,0 +1,18 @@
+#ifndef ZLL_FUNCTIONAL_DETAIL_FNTYPES_HPP
+#define ZLL_FUNCTIONAL_DETAIL_FNTYPES_HPP
+
+namespace zll {
+namespace detail {
+// clang-format off
+template <typename> struct fn_types;
+
+template <typename R> struct fn_types<R()> { typedef R type(); };
+template <typename R> struct fn_types<R() const> { typedef R type(); };
+
+template <typename R, typename T> struct fn_types<R(T)> { typedef R type(T); };
+template <typename R, typename T> struct fn_types<R(T) const> { typedef R type(T); };
+// clang-format on
+}  // namespace detail
+}  // namespace zll
+
+#endif  // ZLL_FUNCTIONAL_DETAIL_FNTYPES_HPP
diff --git a/include/zll/functional/function_ref.hpp b/include/zll/functional/function_ref.hpp
new file mode 100644
index 0000000..15f0633
--- /dev/null
+++ b/include/zll/functional/function_ref.hpp
@@ -0,0 +1,153 @@
+#ifndef ZLL_FUNCTIONAL_FUNCTIONREF_HPP
+#define ZLL_FUNCTIONAL_FUNCTIONREF_HPP
+
+#include "zll/functional/detail/bound_entity_type.hpp"
+#include "zll/functional/detail/fn_types.hpp"
+
+#include "zll/memory/address_of.hpp"
+
+#include "zll/meta/traits/enable_if.hpp"
+#include "zll/meta/traits/is_object.hpp"
+#include "zll/meta/traits/is_function.hpp"
+#include "zll/meta/traits/remove_reference.hpp"
+
+#include "zll/utils/nontype.hpp"
+
+namespace zll {
+namespace detail {
+
+template <typename T, typename U>
+struct fn_enable_if_object {
+    typedef typename zll::meta::enable_if<zll::meta::is_object<T>::value, U>::type type;
+};
+
+template <typename T, typename U>
+struct fn_enable_if_function {
+    typedef typename zll::meta::enable_if<zll::meta::is_function<T>::value, U>::type type;
+};
+
+}  // namespace detail
+
+template <typename SIG_T, typename = typename detail::fn_types<SIG_T>::type>
+class function_ref;
+
+template <typename SIG_T, typename R>
+class function_ref<SIG_T, R()> {
+    typedef detail::bound_entity_type entity_type;
+    typedef R (*thunk_ptr_type)(entity_type);
+
+public:
+    typedef R (*signature_type)();
+
+    template <typename F>
+    explicit function_ref(
+        const F& f, typename zll::meta::enable_if<!(zll::meta::is_member_pointer<F>::value ||
+                                                    zll::is_nontype<typename zll::meta::remove_cvref<F>::type>::value),
+                                                  void*>::type = NULL)
+        : m_bound_entity(zll::addressof(f), detail::bound_entity_object()),
+          m_thunk_ptr(function_ref::thunk_call<typename zll::meta::remove_reference<F>::type>) {}
+
+    template <typename F>
+    explicit function_ref(F* f, typename detail::fn_enable_if_function<F, void*>::type = NULL)
+        : m_bound_entity(f, detail::bound_entity_function()), m_thunk_ptr(function_ref::thunk_fn_call<F>) {}
+
+    template <signature_type VALUE>
+    function_ref(zll::nontype_t<signature_type, VALUE>)
+        : m_bound_entity(), m_thunk_ptr(function_ref::thunk_nontype_call<VALUE>) {}
+
+    template <typename T, T VALUE, typename U>
+    function_ref(zll::nontype_t<T, VALUE>, U& obj)
+        : m_bound_entity(zll::addressof(obj), detail::bound_entity_object()),
+          m_thunk_ptr(function_ref::thunk_member_call<T, VALUE, U>) {}
+
+    R operator()() const { return m_thunk_ptr(m_bound_entity); }
+
+private:
+    template <typename T>
+    static typename zll::meta::enable_if<!(zll::is_nontype<T>::value), R>::type thunk_call(entity_type entity) {
+        T& obj = *detail::get<T>(entity);
+        return obj();
+    }
+
+    template <typename F>
+    static R thunk_fn_call(entity_type entity) {
+        return detail::get<F>(entity)();
+    }
+
+    template <signature_type VALUE>
+    static R thunk_nontype_call(entity_type) {
+        return VALUE();
+    }
+
+    template <typename T, T VALUE, typename U>
+    static R thunk_member_call(entity_type entity) {
+        U& obj = *detail::get<U>(entity);
+        return (obj.*VALUE)();
+    }
+
+    entity_type m_bound_entity;
+    thunk_ptr_type m_thunk_ptr;
+};
+
+template <typename SIG_T, typename R, typename ARG1_T>
+class function_ref<SIG_T, R(ARG1_T)> {
+    typedef detail::bound_entity_type entity_type;
+    typedef R (*thunk_ptr_type)(entity_type, ARG1_T);
+
+public:
+    typedef R (*signature_type)(ARG1_T);
+
+    template <typename F>
+    explicit function_ref(
+        const F& f, typename zll::meta::enable_if<!(zll::meta::is_member_pointer<F>::value ||
+                                                    zll::is_nontype<typename zll::meta::remove_cvref<F>::type>::value),
+                                                  void*>::type = NULL)
+        : m_bound_entity(zll::addressof(f), detail::bound_entity_object()),
+          m_thunk_ptr(function_ref::thunk_call<typename zll::meta::remove_reference<F>::type>) {}
+
+    template <typename F>
+    explicit function_ref(F* f, typename detail::fn_enable_if_function<F, void*>::type = NULL)
+        : m_bound_entity(f, detail::bound_entity_function()), m_thunk_ptr(function_ref::thunk_fn_call<F>) {}
+
+    template <signature_type VALUE>
+    function_ref(zll::nontype_t<signature_type, VALUE>)
+        : m_bound_entity(), m_thunk_ptr(function_ref::thunk_nontype_call<VALUE>) {}
+
+    template <typename T, T VALUE, typename U>
+    function_ref(zll::nontype_t<T, VALUE>, U& obj)
+        : m_bound_entity(zll::addressof(obj), detail::bound_entity_object()),
+          m_thunk_ptr(function_ref::thunk_member_call<T, VALUE, U>) {}
+
+    R operator()(ARG1_T arg) const { return m_thunk_ptr(m_bound_entity, arg); }
+
+private:
+    template <typename T>
+    static typename zll::meta::enable_if<!(zll::is_nontype<T>::value), R>::type thunk_call(entity_type entity,
+                                                                                           ARG1_T arg) {
+        T& obj = *detail::get<T>(entity);
+        return obj(arg);
+    }
+
+    template <typename F>
+    static R thunk_fn_call(entity_type entity, ARG1_T arg) {
+        return detail::get<F>(entity)(arg);
+    }
+
+    template <signature_type VALUE>
+    static R thunk_nontype_call(entity_type, ARG1_T arg) {
+        return VALUE(arg);
+    }
+
+    template <typename T, T VALUE, typename U>
+    static R thunk_member_call(entity_type entity, ARG1_T arg) {
+        U& obj = *detail::get<U>(entity);
+        return (obj.*VALUE)(arg);
+    }
+
+    entity_type m_bound_entity;
+    thunk_ptr_type m_thunk_ptr;
+};
+
+}  // namespace zll
+
+#endif  // ZLL_FUNCTIONAL_FUNCTIONREF_HPP
diff --git a/tests/unit_tests/functional/function_ref_tests.cpp b/tests/unit_tests/functional/function_ref_tests.cpp
new file mode 100644
index 0000000..0385236
--- /dev/null
+++ b/tests/unit_tests/functional/function_ref_tests.cpp
@@ -0,0 +1,112 @@
+#include <zll/functional/function_ref.hpp>
+#include <zll/utils/typeof_macro.hpp>
+
+#include <utest.h>
+
+struct functor1 {
+    int operator()() const { return 17; }
+};
+
+int free_fun1() { return 42; }
+
+struct static_fun {
+    static int fun() { return 15; }
+};
+
+struct member_fun {
+    int fun() const { return 3; }
+};
+
+UTEST(functional_function_ref, no_parameter) {
+    {
+        functor1 fun;
+        zll::function_ref<int() const> fn_ref(fun);
+
+        ASSERT_EQ(fn_ref(), 17);
+    }
+    {
+        const functor1 fun;
+        zll::function_ref<int() const> fn_ref(fun);
+
+        ASSERT_EQ(fn_ref(), 17);
+    }
+    {
+        zll::function_ref<int()> fn_ref(free_fun1);
+        ASSERT_EQ(fn_ref(), 42);
+    }
+    {
+        zll::function_ref<int()> fn_ref(&free_fun1);
+        ASSERT_EQ(fn_ref(), 42);
+    }
+    {
+        zll::nontype_t<int (*)(), free_fun1> nontype;
+        zll::function_ref<int()> fn_ref(nontype);
+        ASSERT_EQ(fn_ref(), 42);
+    }
+    {
+        zll::nontype_t<int (*)(), static_fun::fun> nontype;
+        zll::function_ref<int()> fn_ref(nontype);
+        ASSERT_EQ(fn_ref(), 15);
+    }
+    {
+        zll::nontype_t<ZLL_TYPE_OF(&member_fun::fun), &member_fun::fun> nontype;
+
+        member_fun obj;
+        zll::function_ref<int()> fn_ref(nontype, obj);
+        ASSERT_EQ(fn_ref(), 3);
+    }
+}
+
+struct functor2 {
+    int operator()(int a) const { return a; }
+};
+
+int free_fun2(char) { return 42; }
+
+struct static_fun2 {
+    static int fun(int a) { return a; }
+};
+
+struct member_fun2 {
+    int fun(int a) const { return a; }
+};
+
+UTEST(functional_function_ref, one_parameter) {
+    {
+        functor2 fun;
+        zll::function_ref<int(int) const> fn_ref(fun);
+
+        ASSERT_EQ(fn_ref(5), 5);
+    }
+    {
+        const functor2 fun;
+        zll::function_ref<int(int) const> fn_ref(fun);
+
+        ASSERT_EQ(fn_ref(8), 8);
+    }
+    {
+        zll::function_ref<int(char)> fn_ref(free_fun2);
+        ASSERT_EQ(fn_ref('a'), 42);
+    }
+    {
+        zll::function_ref<int(char)> fn_ref(&free_fun2);
+        ASSERT_EQ(fn_ref('f'), 42);
+    }
+    {
+        zll::nontype_t<int (*)(char), free_fun2> nontype;
+        zll::function_ref<int(char)> fn_ref(nontype);
+        ASSERT_EQ(fn_ref('g'), 42);
+    }
+    {
+        zll::nontype_t<int (*)(int), static_fun2::fun> nontype;
+        zll::function_ref<int(int)> fn_ref(nontype);
+        ASSERT_EQ(fn_ref(11), 11);
+    }
+    {
+        zll::nontype_t<ZLL_TYPE_OF(&member_fun2::fun), &member_fun2::fun> nontype;
+
+        member_fun2 obj;
+        zll::function_ref<int(int)> fn_ref(nontype, obj);
+        ASSERT_EQ(fn_ref(-12), -12);
+    }
+}
diff --git a/tests/unit_tests/meson.build b/tests/unit_tests/meson.build
index f397a04..e8a0094 100644
--- a/tests/unit_tests/meson.build
+++ b/tests/unit_tests/meson.build
@@ -1,5 +1,7 @@
 
 unit_tests_srcs = [
+    'functional/function_ref_tests.cpp',
+    
     'memory/address_of_tests.cpp',
     
     'meta/integral_constant_tests.cpp',