From 8933209df44b7f5fecd9a0af478992e06034ac6f Mon Sep 17 00:00:00 2001
From: klaus triendl <klaus@triendl.eu>
Date: Wed, 15 Nov 2023 21:35:23 +0200
Subject: [PATCH] Operators for user-defined functions

---
 dev/function.h                       | 5 +++++
 include/sqlite_orm/sqlite_orm.h      | 6 ++++++
 tests/static_tests/operators_adl.cpp | 5 +++++
 3 files changed, 16 insertions(+)

diff --git a/dev/function.h b/dev/function.h
index f8cd7efe3..469423f93 100644
--- a/dev/function.h
+++ b/dev/function.h
@@ -7,6 +7,7 @@
 
 #include "functional/cxx_universal.h"
 #include "functional/cxx_type_traits_polyfill.h"
+#include "tags.h"
 
 namespace sqlite_orm {
 
@@ -86,6 +87,10 @@ namespace sqlite_orm {
             args_tuple args;
         };
 
+        template<class T>
+        SQLITE_ORM_INLINE_VAR constexpr bool
+            is_operator_argument_v<T, std::enable_if_t<polyfill::is_specialization_of_v<T, function_call>>> = true;
+
         template<class T>
         struct unpacked_arg {
             using type = T;
diff --git a/include/sqlite_orm/sqlite_orm.h b/include/sqlite_orm/sqlite_orm.h
index 6006bb768..ff98d125e 100644
--- a/include/sqlite_orm/sqlite_orm.h
+++ b/include/sqlite_orm/sqlite_orm.h
@@ -10865,6 +10865,8 @@ namespace sqlite_orm {
 
 // #include "functional/cxx_type_traits_polyfill.h"
 
+// #include "tags.h"
+
 namespace sqlite_orm {
 
     struct arg_values;
@@ -10943,6 +10945,10 @@ namespace sqlite_orm {
             args_tuple args;
         };
 
+        template<class T>
+        SQLITE_ORM_INLINE_VAR constexpr bool
+            is_operator_argument_v<T, std::enable_if_t<polyfill::is_specialization_of_v<T, function_call>>> = true;
+
         template<class T>
         struct unpacked_arg {
             using type = T;
diff --git a/tests/static_tests/operators_adl.cpp b/tests/static_tests/operators_adl.cpp
index 2c8a3c200..23335cf60 100644
--- a/tests/static_tests/operators_adl.cpp
+++ b/tests/static_tests/operators_adl.cpp
@@ -10,6 +10,7 @@ using sqlite_orm::and_;
 using sqlite_orm::c;
 using sqlite_orm::colalias_a;
 using sqlite_orm::column;
+using sqlite_orm::func;
 using sqlite_orm::get;
 using sqlite_orm::or_;
 using sqlite_orm::internal::and_condition_t;
@@ -107,11 +108,15 @@ TEST_CASE("ADL and expression operators") {
     struct User {
         int id;
     };
+    struct ScalarFunction {
+        int operator()() const;
+    };
 
     runTests(c(&User::id));
     runTests(column<User>(&User::id));
     runTests(get<colalias_a>());
     runTests(alias_column<alias_a<User>>(&User::id));
+    runTests(func<ScalarFunction>());
 #ifdef SQLITE_ORM_WITH_CPP20_ALIASES
     runTests("a"_col);
 #endif