Filtered visitor (#18)

New `visit()` overload taking a filter.

Closes #17.

include/cppast/visitor.hpp

@@ -5,10 +5,11 @@
 #ifndef CPPAST_VISITOR_HPP_INCLUDED
 #define CPPAST_VISITOR_HPP_INCLUDED
 
+#include <cppast/cpp_entity.hpp>
+#include <cppast/cpp_entity_kind.hpp>
+
 namespace cppast
 {
-    class cpp_entity;
-
     /// Information about the state of a visit operation.
     struct visitor_info
     {
@@ -31,7 +32,8 @@ namespace cppast
     /// \exclude
     namespace detail
     {
-        using visitor_callback_t = bool (*)(void* mem, const cpp_entity&, visitor_info info);
+        using visitor_callback_t  = bool (*)(void* mem, const cpp_entity&, visitor_info info);
+        using visitor_predicate_t = bool (*)(const cpp_entity&);
 
         template <typename Func>
         bool visitor_callback(void* mem, const cpp_entity& e, visitor_info info)
@@ -54,6 +56,52 @@ namespace cppast
     {
         detail::visit(e, &detail::visitor_callback<Func>, &f, false);
     }
+
+    /// Visits a [cppast::cpp_entity]().
+    /// \effects Invokes the callback for the current entity,
+    /// and child entities that match the given predicate.
+    /// It will pass a reference to the current entity and the [cppast::visitor_info]().
+    /// The return value of the callback controls the visit operation,
+    /// the semantic depend on the [cppast::visitor_info::event_type]().
+    template <typename Func, typename Predicate>
+    void visit(const cpp_entity& e, Predicate pred, Func f)
+    {
+        visit(e, [&](const cpp_entity& e, visitor_info& info) {
+            if (pred(e))
+                return f(e, info);
+            return true;
+        });
+    }
+
+    /// Generates, at compile-time, a predicate that returns true iff the
+    /// given entity holds one of the [cppast::cpp_entity_kind]()s specified
+    /// in paramaters of the blacklist template.
+    template <cpp_entity_kind... K>
+    detail::visitor_predicate_t whitelist()
+    {
+        static_assert(sizeof...(K) > 0, "At least one entity kind should be specified");
+        return [](const cpp_entity& e) {
+            bool result = false;
+            // this ugliness avoids recursive expansion which would be required in C++11,
+            // otherwise known as poor man's fold expression.
+            (void)std::initializer_list<int>{(result = result || (K == e.kind()), 0)...};
+            return result;
+        };
+    }
+
+    /// Generates, at compile-time, a predicate that returns true iff the
+    /// given entity holds a [cppast::cpp_entity_kind]() that's different
+    /// from all of those specified in the paramaters of the blacklist template.
+    template <cpp_entity_kind... K>
+    detail::visitor_predicate_t blacklist()
+    {
+        static_assert(sizeof...(K) > 0, "At least one entity kind should be specified");
+        return [](const cpp_entity& e) {
+            bool result = true;
+            (void)std::initializer_list<int>{(result = result && (K != e.kind()), 0)...};
+            return result;
+        };
+    }
 } // namespace cppast
 
 #endif // CPPAST_VISITOR_HPP_INCLUDED