Partially address #2201

examples/cppx/Interface.cpp

@@ -1,29 +1,36 @@
+#include <experimental/meta>
+#include <experimental/compiler>
+
+using namespace std::experimental;
 
 //====================================================================
 // Library code: implementing the metaclass (once)
 
-$class interface {
-    constexpr {
-        compiler.require($interface.variables().empty(),
-                         "interfaces may not contain data");
-        for... (auto f : $interface.functions()) {
-            compiler.require(!f.is_copy() && !f.is_move(),
-                "interfaces may not copy or move; consider a"
-                " virtual clone() instead");
-            if (!f.has_access()) f.make_public();
-            compiler.require(f.is_public(),
-                "interface functions must be public");
-            f.make_pure_virtual();
-        }
-    }
-    virtual ~interface() noexcept { }
+consteval void interface(meta::info source) {
+  for (meta::info mem : meta::member_range(source)) {
+    meta::compiler.require(!meta::is_data_member(mem), "interfaces may not contain data");
+    meta::compiler.require(!meta::is_copy(mem) && !meta::is_move(mem),
+       "interfaces may not copy or move; consider"
+       " a virtual clone() instead");
+
+    if (meta::has_default_access(mem))
+      meta::make_public(mem);
+
+    meta::compiler.require(meta::is_public(mem), "interface functions must be public");
+
+    meta::make_pure_virtual(mem);
+
+    -> mem;
+  }
+
+  -> fragment struct X { virtual ~X() noexcept {} };
 };
 
 
 //====================================================================
 // User code: using the metaclass to write a type (many times)
 
-interface Shape {
+class(interface) Shape {
     int area() const;
     void scale_by(double factor);
 };
@@ -37,12 +44,10 @@ interface Shape {
     // Shape(const Shape&); // error: interfaces may not copy or move;
     //                      //        consider a virtual clone() instead
 
-// Godbolt.org note: Click the "triangle ! icon" to see the output
-constexpr {
-    compiler.debug($Shape);
+consteval {
+  meta::compiler.print(reflexpr(Shape));
 }
 
-
 //====================================================================
 // And then continue to use it as "just a class" as always... this is
 // normal code just as if we'd written Shape not using a metaclass
@@ -53,6 +58,10 @@ public:
     void scale_by(double factor) override { }
 };
 
+consteval {
+  meta::compiler.print(reflexpr(Circle));
+}
+
 #include <memory>
 
 int main() {

examples/cppx/Interface_(CppCon_2017).cpp

@@ -0,0 +1,61 @@
+
+//====================================================================
+// Library code: implementing the metaclass (once)
+
+$class interface {
+    constexpr {
+        compiler.require($interface.variables().empty(),
+                         "interfaces may not contain data");
+        for... (auto f : $interface.functions()) {
+            compiler.require(!f.is_copy() && !f.is_move(),
+                "interfaces may not copy or move; consider a"
+                " virtual clone() instead");
+            if (!f.has_access()) f.make_public();
+            compiler.require(f.is_public(),
+                "interface functions must be public");
+            f.make_pure_virtual();
+        }
+    }
+    virtual ~interface() noexcept { }
+};
+
+
+//====================================================================
+// User code: using the metaclass to write a type (many times)
+
+interface Shape {
+    int area() const;
+    void scale_by(double factor);
+};
+
+    // try putting any of these lines into Shape to see "interface" rules
+    // enforced => using the metaclass name to declare intent makes
+    // this code more robust to such changes under maintenance
+    //
+    // int i;               // error: interfaces may not contain data
+    // private: void g();   // error: interface functions must be public
+    // Shape(const Shape&); // error: interfaces may not copy or move;
+    //                      //        consider a virtual clone() instead
+
+// Godbolt.org note: Click the "triangle ! icon" to see the output
+constexpr {
+    compiler.debug($Shape);
+}
+
+
+//====================================================================
+// And then continue to use it as "just a class" as always... this is
+// normal code just as if we'd written Shape not using a metaclass
+
+class Circle : public Shape {
+public:
+    int area() const override { return 1; }
+    void scale_by(double factor) override { }
+};
+
+#include <memory>
+
+int main() {
+    std::unique_ptr<Shape> shape = std::make_unique<Circle>();
+    shape->area();
+}

examples/cppx/Value_(CppCon_2017).cpp

@@ -0,0 +1,47 @@
+//====================================================================
+// Library code: implementing the metaclass (once)
+
+$class basic_value {
+    basic_value() = default;
+    basic_value(const basic_value& that) = default;
+    basic_value(basic_value&& that) = default;
+    basic_value& operator=(const basic_value& that) = default;
+    basic_value& operator=(basic_value&& that) = default;
+
+    constexpr {
+        for... (auto f : $basic_value.variables())
+            if (!f.has_access()) f.make_private();
+        for... (auto f : $basic_value.functions()) {
+            if (!f.has_access()) f.make_public();
+            compiler.require(!f.is_protected(), "a value type may not have a protected function");
+            compiler.require(!f.is_virtual(),   "a value type may not have a virtual function");
+            compiler.require(!f.is_destructor() || f.is_public(), "a value destructor must be public");
+        }
+    }
+};
+
+$class value : basic_value { };
+
+
+//====================================================================
+// User code: using the metaclass to write a type (many times)
+
+value Point {
+    int x = 0, y = 0;
+    Point(int xx, int yy) : x{xx}, y{yy} { }
+};
+
+Point get_some_point() { return {1,1}; }
+
+int main() {
+
+    Point p1(50,100), p2;
+    p2 = get_some_point();
+    p2.x = 42;
+
+}
+
+// Compiler Explorer note: Click the "triangle ! icon" to see the output:
+constexpr {
+    compiler.debug($Point);
+}

examples/cppx/default.cpp

@@ -1,47 +1,2 @@
-//====================================================================
-// Library code: implementing the metaclass (once)
-
-$class basic_value {
-    basic_value() = default;
-    basic_value(const basic_value& that) = default;
-    basic_value(basic_value&& that) = default;
-    basic_value& operator=(const basic_value& that) = default;
-    basic_value& operator=(basic_value&& that) = default;
-
-    constexpr {
-        for... (auto f : $basic_value.variables())
-            if (!f.has_access()) f.make_private();
-        for... (auto f : $basic_value.functions()) {
-            if (!f.has_access()) f.make_public();
-            compiler.require(!f.is_protected(), "a value type may not have a protected function");
-            compiler.require(!f.is_virtual(),   "a value type may not have a virtual function");
-            compiler.require(!f.is_destructor() || f.is_public(), "a value destructor must be public");
-        }
-    }
-};
-
-$class value : basic_value { };
-
-
-//====================================================================
-// User code: using the metaclass to write a type (many times)
-
-value Point {
-    int x = 0, y = 0;
-    Point(int xx, int yy) : x{xx}, y{yy} { }
-};
-
-Point get_some_point() { return {1,1}; }
-
-int main() {
-
-    Point p1(50,100), p2;
-    p2 = get_some_point();
-    p2.x = 42;
-
-}
-
-// Compiler Explorer note: Click the "triangle ! icon" to see the output:
-constexpr {
-    compiler.debug($Point);
-}
+// Pick an appropriate example from the Load/Save
+// icon above.