OSX/libsecurity_utilities/lib/typedvalue.h

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  23
  24
  25 //
  26 // typedvalue - type-safe reference transmission of arbitrary types.
  27 //
  28 // This slight-of-hand pair of classes allows arbitrary types to be passed through an API
  29 // without losing C++ type safety. Specifically, the type is encapsulated in C++ polymorphism,
  30 // and can be resolved through the C++ typeinfo/dynamic_cast system in a fairly
  31 // convenient way. This is intended to replace passing (void *) arguments around.
  32 // It is obviously not meant to replace proper class hierarchies in APIs.
  33 //
  34 #ifndef _H_TYPEDVALUE
  35 #define _H_TYPEDVALUE
  36
  37 #include <security_utilities/utilities.h>
  38 #include <security_utilities/debugging.h>
  39
  40
  41 namespace Security {
  42
  43
  44 //
  45 // A GenericValue can represent any (one) type. Note the template assignment
  46 // that works *only* for the type it actually represents. Note particularly that
  47 // no automatic conversions are made (other than to subclass).
  48 //
  49 class GenericValue {
  50 public:
  51     virtual ~GenericValue();
  52
  53     template <class V>
  54     void operator = (const V &value);
  55 };
  56
  57
  58 //
  59 // A TypedValue is a particular typed instance of a GenericValue
  60 //
  61 template <class Value>
  62 class TypedValue : public GenericValue {
  63 public:
  64     TypedValue() : mValue() { }
  65     TypedValue(const Value &v) : mValue(v) { }
  66     Value &value()                                      { return mValue; }
  67     operator Value &()                          { return mValue; }
  68     void operator = (const Value &value) { mValue = value; }
  69
  70 private:
  71     Value mValue;
  72 };
  73
  74
  75 //
  76 // The polymorphic assignment access method
  77 //
  78 template <class Value>
  79 void GenericValue::operator = (const Value &value)
  80 { safer_cast<TypedValue<Value> &>(*this) = value; }
  81
  82
  83 }       // end namespace Security
  84
  85
  86 #endif //_H_TYPEDVALUE