/// <summary>
/// Gets the DuckProxyType<TInterface> object for a given duck type.
/// </summary>
/// <remarks>
/// First, the most general type in the inheritance chain of the given type that implements all the
/// members of TInterface is selected. Then if a proxy type has already been generated, it returns
/// it. Finally, if not, it creates a new object and adds it to the dictionary.
/// </remarks>
/// <param name="duckType">Type of object being casted.</param>
/// <returns>The duck proxy type to use to cast or prepare for casting.</returns>
private static DuckProxyType <TInterface> GetProxyType(Type duckType)
{
DuckProxyType <TInterface> proxyType = null;
// Examine the duck type's inheritance chain.
List <Type> inheritanceChain = new List <Type>();
Type baseType = duckType;
do
{
inheritanceChain.Add(baseType);
baseType = baseType.BaseType;
}while (baseType != null);
// Iterate the inheritance chain backwards (most general to most specialized) to find a proxy type
// that has already been generated.
for (int i = inheritanceChain.Count - 1; i >= 0; i--)
{
Type type = inheritanceChain[i];
if (s_ProxyTypes.ContainsKey(type))
{
proxyType = s_ProxyTypes[type];
break;
}
}
if (proxyType == null)
{
// Iterate the inheritance chain backwards (most general to most specialized) to find the most
// general type that can be casted to TInterface.
for (int i = inheritanceChain.Count - 1; i >= 0; i--)
{
Type type = inheritanceChain[i];
if (CanCast(type))
{
proxyType = new DuckProxyType <TInterface>(type);
break;
}
}
if (proxyType == null)
{
// If proxyType is null, then DuckTyping.CanCast<>() returned false for every type in the
// inheritance chain. The following line will cause an exception to be thrown when
// GenerateProxyType() is called. The exception will indicate why the duck cannot be casted.
proxyType = new DuckProxyType <TInterface>(duckType);
}
else
{
// If we got to this point, the cast is valid and it is ok to add the proxy type to the dictionary.
s_ProxyTypes.Add(proxyType.m_DuckType, proxyType);
}
}
return(proxyType);
}
/// <summary>
/// Calls the static WrapDuck method of the generated proxy type to initialize a new instance of
/// the proxy type with a given duck object.
/// </summary>
/// <param name="duck">Duck object that the new proxy object should forward calls to.</param>
/// <returns>
/// An instance of the proxy type, which implements TInterface, initialized with the given duck
/// object.
/// </returns>
internal static TInterface WrapDuck(object duck)
{
DuckProxyType <TInterface> proxyType = GetProxyType(duck.GetType());
// Make sure the proxy type is generated before we try to call it.
proxyType.GenerateProxyType();
// Call wrap method in the proxy type to create an instance of the proxy for the duck and return it.
return(proxyType.m_WrapDuck(duck));
}
