2 files changed, 53 insertions, 18 deletions

diff --git a/src/core/model/Typesystem.cpp b/src/core/model/Typesystem.cpp
index 591dcbe..dc6df63 100644
--- a/src/core/model/Typesystem.cpp
+++ b/src/core/model/Typesystem.cpp
@@ -26,7 +26,10 @@ namespace ousia {
 
 /* Static helper functions */
 
-static void NullMagicCallback(Variant &, bool, ManagedUid) {}
+static Type::MagicCallbackResult NullMagicCallback(Variant &, const Type *)
+{
+	return Type::MagicCallbackResult::NOT_FOUND;
+}
 
 /* Class Type */
 
@@ -35,13 +38,18 @@ bool Type::build(Variant &data, Logger &logger,
 {
 	// If the given variant is marked as "magic", try to resolve the real value
 	if (data.isMagic()) {
-		Variant strData = Variant::fromString(data.asString());
-		Logger nullLogger;
-		bool valid = isValid(strData, nullLogger);
-		magicCallback(data, valid,
-		              getUid());
-		build(strData, nullLogger);
-		return true;  // Just return true for now
+		switch (magicCallback(data, this)) {
+			case MagicCallbackResult::NOT_FOUND:
+				break;
+			case MagicCallbackResult::FOUND_INVALID: {
+				// The magic callback has probably already issued an error
+				// message -- do not print more errors
+				Logger nullLogger;
+				return build(data, nullLogger);
+			}
+			case MagicCallbackResult::FOUND_VALID:
+				return true;
+		}
 	}
 
 	try {
@@ -216,6 +224,10 @@ void Attribute::setDefaultValue(const Variant &defaultValue, Logger &logger)
 	initialize(logger);
 }
 
+const Variant &Attribute::getDefaultValue() const { return defaultValue; }
+
+Variant &Attribute::getDefaultValue() { return defaultValue; }
+
 void Attribute::removeDefaultValue()
 {
 	invalidate();
@@ -224,6 +236,8 @@ void Attribute::removeDefaultValue()
 	optional = false;
 }
 
+bool Attribute::isOptional() const { return optional; }
+
 void Attribute::setType(Handle<Type> type, Logger &logger)
 {
 	invalidate();
@@ -232,6 +246,8 @@ void Attribute::setType(Handle<Type> type, Logger &logger)
 	initialize(logger);
 }
 
+Rooted<Type> Attribute::getType() const { return type; }
+
 /* Class StructType */
 
 bool StructType::resolveIndexKey(const std::string &key, size_t &idx) const
@@ -591,6 +607,8 @@ void Constant::setType(Handle<Type> type, Logger &logger)
 	this->type->build(this->value, logger);
 }
 
+const Variant &Constant::getValue() const { return value; }
+
 Variant &Constant::getValue() { return value; }
 
 void Constant::setValue(Variant value, Logger &logger)
diff --git a/src/core/model/Typesystem.hpp b/src/core/model/Typesystem.hpp
index d88a7e9..9d85d80 100644
--- a/src/core/model/Typesystem.hpp
+++ b/src/core/model/Typesystem.hpp
@@ -57,19 +57,21 @@ class SystemTypesystem;
  */
 class Type : public Node {
 public:
+	enum class MagicCallbackResult { NOT_FOUND, FOUND_INVALID, FOUND_VALID };
+
 	/**
 	 * Callback function called when a variant with "magic" value is reached.
 	 * This callback allows to transform these magic values into something else.
 	 * This mechanism is used to resolve constants.
 	 *
-	 * @param data is the magic value that should be looked up.
-	 * @param isValid is set to true if the magic value does not necessarily
-	 * have to be looked up, in this case no error message has to be generated
-	 * if the lookup for a constant fails.
-	 * @param type is the managed uid of the underlying Type for which the magic
-	 * value should be looked up.
+	 * @param data is the magic value that should be looked up and the variant
+	 * to which the value of the looked up constant should be written.
+	 * @param type is a const pointer at the type. TODO: Replace this with a
+	 * "ConstHandle".
+	 * @return true if a constant was found, false otherwise.
 	 */
-	using MagicCallback = std::function<void(Variant &data, bool isValid, ManagedUid Type)>;
+	using MagicCallback =
+	    std::function<MagicCallbackResult(Variant &data, const Type *type)>;
 
 protected:
 	/**
@@ -503,7 +505,14 @@ public:
 	 * @return the default value of the attribute. If no default value has been
 	 * given a null variant is returned (the opposite does not hold).
 	 */
-	Variant& getDefaultValue() { return defaultValue; }
+	const Variant &getDefaultValue() const;
+
+	/**
+	 * Returns a reference at the default value.
+	 *
+	 * @return a reference at the default value of the attribute.
+	 */
+	Variant &getDefaultValue();
 
 	/**
 	 * Removes any default value from the attribute, making this attribute
@@ -517,7 +526,7 @@ public:
 	 *
 	 * @return true if the attribute is optional, false otherwise.
 	 */
-	bool isOptional() const { return optional; }
+	bool isOptional() const;
 
 	/**
 	 * Sets the type of the attribute to the specified value. This will
@@ -536,7 +545,7 @@ public:
 	 *
 	 * @return the underlying type of the Rooted object.
 	 */
-	Rooted<Type> getType() const { return type; }
+	Rooted<Type> getType() const;
 };
 
 /**
@@ -992,6 +1001,14 @@ public:
 	 *
 	 * @return a const reference to the actual value of the constant.
 	 */
+	const Variant &getValue() const;
+
+	/**
+	 * Returns a reference pointing at the value of the constant. The value must
+	 * be interpreted with the help of the type of the constant.
+	 *
+	 * @return a reference to the actual value of the constant.
+	 */
 	Variant &getValue();
 
 	/**