Add struct meta function, another from P0707 section 3

It's simpler than in P0707 though because of Cpp2's `operator=` unification

Author: hsutter

regression-tests/pure2-types-ordering-via-meta-functions.cpp2

@@ -14,6 +14,10 @@ person_in_family_tree: @partially_ordered type = {
     operator=: (out this, parents: int) = { dummy_data = parents; }
 }
 
+mystruct: @struct type = {
+    val: int = 0;
+}
+
 main: () = {
     a: my_integer = 1;
     b: my_integer = 2;
@@ -41,4 +45,6 @@ main: () = {
     else {
         std::cout << "more\n";
     }
+
+    s: mystruct = ();
 }

regression-tests/test-results/pure2-types-ordering-via-meta-functions.cpp

@@ -19,6 +19,10 @@ class case_insensitive_string;
 class person_in_family_tree;
 
 
+#line 17 "pure2-types-ordering-via-meta-functions.cpp2"
+class mystruct;
+    
+
 //=== Cpp2 type definitions and function declarations ===========================
 
 
@@ -62,6 +66,18 @@ public: [[nodiscard]] auto operator<=>(person_in_family_tree const& that) const
 #line 15 "pure2-types-ordering-via-meta-functions.cpp2"
 };
 
+class mystruct {
+    public: int val {0}; 
+    public: mystruct(mystruct const& that);
+
+public: auto operator=(mystruct const& that) -> mystruct& ;
+public: mystruct(mystruct&& that);
+public: auto operator=(mystruct&& that) -> mystruct& ;
+public: mystruct();
+
+#line 19 "pure2-types-ordering-via-meta-functions.cpp2"
+};
+
 auto main() -> int;
 
 
@@ -103,8 +119,21 @@ auto main() -> int;
                                             return *this;
 #line 14 "pure2-types-ordering-via-meta-functions.cpp2"
     }
-
-#line 17 "pure2-types-ordering-via-meta-functions.cpp2"
+    
+    mystruct::mystruct(mystruct const& that)
+                                : val{ that.val }{}
+
+    auto mystruct::operator=(mystruct const& that) -> mystruct& {
+                                val = that.val;
+                                return *this;}
+    mystruct::mystruct(mystruct&& that)
+                                : val{ std::move(that).val }{}
+    auto mystruct::operator=(mystruct&& that) -> mystruct& {
+                                val = std::move(that).val;
+                                return *this;}
+    
+    mystruct::mystruct(){}
+#line 21 "pure2-types-ordering-via-meta-functions.cpp2"
 auto main() -> int{
     my_integer a {1}; 
     my_integer b {2}; 
@@ -132,5 +161,7 @@ auto main() -> int{
     else {
         std::cout << "more\n";
     }
+
+    mystruct s {}; 
 }
 

source/cppfront.cpp

@@ -1531,15 +1531,11 @@ class cppfront
             printer.print_cpp2("cpp2::", pos);
         }
 
-        //  'new' is a named allocator object
-        if (n == "new") {
-            printer.print_cpp2("cpp2_new", pos);
-        }
         //  'this' is not a pointer
-        else if (n == "this") {
+        if (n == "this") {
             printer.print_cpp2("(*this)", pos);
         }
-        //  Reclaim the alternative names for users
+        //  Reclaim the alternative names and some keywords for users
         else if (
             n == "and"
             || n == "and_eq"
@@ -1552,6 +1548,8 @@ class cppfront
             || n == "or_eq"
             || n == "xor"
             || n == "xor_eq"
+            || n == "new"
+            || n == "struct"
             )
         {
             printer.print_cpp2("cpp2_"+n.to_string(true), pos);

source/lex.h

@@ -942,7 +942,7 @@ auto lex_line(
             "^operator|"
             "^private|^protected|^public|"
             "^register|^reinterpret_cast|^requires|^return|"
-            "^short|^signed|^sizeof|^static_assert|^static_cast|^static|^struct|^switch|"
+            "^short|^signed|^sizeof|^static_assert|^static_cast|^static|^switch|"
             "^template|^this|^thread_local|^throws|^throw|^try|^typedef|^typeid|^typename|"
             "^unsigned|^using|"
             "^virtual|^void|^volatile|"

source/reflect.h

@@ -682,6 +682,50 @@ auto partially_ordered_value(meta::type_declaration& t)
 }
 
 
+//-----------------------------------------------------------------------
+// 
+//     "By definition, a `struct` is a `class` in which members
+//      are by default `public`; that is,
+//
+//      	struct s { ...
+// 
+//      is simply shorthand for
+//
+//          class s { public: ...
+//
+//      ... Which style you use depends on circumstances and taste.
+//      I usually prefer to use `struct` for classes that have all
+//      data `public`."
+// 
+//          -- Stroustrup (The C++ Programming Language, 3rd ed., p. 234)
+//
+//-----------------------------------------------------------------------
+// 
+//  struct
+//
+//  a basic_value with only public bases, objects, and functions,
+//  no virtual functions, and no user-defined constructors
+//  (i.e., no invariants) or assignment or destructors.
+//
+auto struct_(meta::type_declaration& t)
+    -> void
+{
+    for (auto m : t.get_members())
+    {
+        m.require( m.make_public(),
+                   "all struct members must be public");
+        if (m.is_function()) {
+            auto mf = m.as_function();
+            t.require( !mf.is_virtual(),
+                       "a struct may not have a virtual function");
+            t.require( !mf.has_name("operator="),
+                       "a struct may not have a user-defined operator=");
+        }
+    }
+    basic_value(t);		// a plain_struct is-a basic_value
+}
+
+
 //-----------------------------------------------------------------------
 //
 //  Now finish the rest of the parser definition
@@ -727,8 +771,11 @@ auto parser::apply_type_meta_functions( declaration_node& n )
         else if (meta->to_string() == "partially_ordered_value") {
             partially_ordered_value( rtype );
         }
+        else if (meta->to_string() == "struct") {
+            struct_( rtype );
+        }
         else {
-            error( "(temporary alpha limitation) unrecognized meta function name '" + meta->to_string() + "' - currently the supported names are: interface, polymorphic_base, ordered, weakly_ordered, partially_ordered, value, weakly_ordered_value, partially_ordered_value" );
+            error( "(temporary alpha limitation) unrecognized meta function name '" + meta->to_string() + "' - currently the supported names are: interface, polymorphic_base, ordered, weakly_ordered, partially_ordered, value, weakly_ordered_value, partially_ordered_value, struct" );
             return false;
         }
     }