Security-55163.44.tar.gz

[apple/security.git] / libsecurity_utilities / lib / typedvalue.h

diff --git a/libsecurity_utilities/lib/typedvalue.h b/libsecurity_utilities/lib/typedvalue.h
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+/*
+ * Copyright (c) 2000-2001,2003-2004 Apple Computer, Inc. All Rights Reserved.
+ * 
+ * @APPLE_LICENSE_HEADER_START@
+ * 
+ * This file contains Original Code and/or Modifications of Original Code
+ * as defined in and that are subject to the Apple Public Source License
+ * Version 2.0 (the 'License'). You may not use this file except in
+ * compliance with the License. Please obtain a copy of the License at
+ * http://www.opensource.apple.com/apsl/ and read it before using this
+ * file.
+ * 
+ * The Original Code and all software distributed under the License are
+ * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
+ * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
+ * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
+ * Please see the License for the specific language governing rights and
+ * limitations under the License.
+ * 
+ * @APPLE_LICENSE_HEADER_END@
+ */
+
+
+//
+// typedvalue - type-safe reference transmission of arbitrary types.
+//
+// This slight-of-hand pair of classes allows arbitrary types to be passed through an API
+// without losing C++ type safety. Specifically, the type is encapsulated in C++ polymorphism,
+// and can be resolved through the C++ typeinfo/dynamic_cast system in a fairly
+// convenient way. This is intended to replace passing (void *) arguments around.
+// It is obviously not meant to replace proper class hierarchies in APIs.
+//
+#ifndef _H_TYPEDVALUE
+#define _H_TYPEDVALUE
+
+#include <security_utilities/utilities.h>
+#include <security_utilities/debugging.h>
+
+
+namespace Security {
+
+
+//
+// A GenericValue can represent any (one) type. Note the template assignment
+// that works *only* for the type it actually represents. Note particularly that
+// no automatic conversions are made (other than to subclass).
+//
+class GenericValue {
+public:
+    virtual ~GenericValue();
+    
+    template <class V>
+    void operator = (const V &value);
+};
+
+
+//
+// A TypedValue is a particular typed instance of a GenericValue
+//
+template <class Value>
+class TypedValue : public GenericValue {
+public:
+    TypedValue() : mValue() { }
+    TypedValue(const Value &v) : mValue(v) { }
+    Value &value()                                     { return mValue; }
+    operator Value &()                         { return mValue; }
+    void operator = (const Value &value) { mValue = value; }
+    
+private:
+    Value mValue;
+};
+
+
+//
+// The polymorphic assignment access method
+//
+template <class Value>
+void GenericValue::operator = (const Value &value)
+{ safer_cast<TypedValue<Value> &>(*this) = value; }
+
+
+}      // end namespace Security
+
+
+#endif //_H_TYPEDVALUE