Yesterday I presented a problem that I struggle with for several hours: given a generic Func<T,object> created by a fluent DSL, how can I call a method that only accepts a non-generic Func<object,object>?  The answer is actually quite simple.

Here’s the relevant non-compiling code from yesterday:

internal interface ISerializationConfig
{
    ...
    void SerializePropertyAsElementUsing(Type target, 
             PropertyInfo property, 
             string elementName, 
             Func<object, object> converter);
}


... 

ITypeSerializationSpec<T> IInitialPropertySerializationSpec<T>.Using(Func<T, object> selector)
{
    //_config is of type ISerializationConfig. 
    _config.SerializePropertyAsElementUsing(typeof(T), 
               _expression.GetProperty(), 
               _expression.GetProperty().Name, 
               /*ERROR:*/ selector);
    return this;
}

...

The answer is actually so simple that I felt dumb for not seeing it immediately.  We can wrap our generic Func<T,object> inside a non-generic Func<object,object>.  The wrapper Func basically serves as an adapter, enabling us to pass an instance of one type to a method that only accepts an instance of another type:

ITypeSerializationSpec<T> IInitialPropertySerializationSpec<T>.Using(Func<T, object> selector)
{
    Func<object,object> wrapper = o => selector((T)o);
    
    //_config is of type ISerializationConfig. 
    _config.SerializePropertyAsElementUsing(typeof(T), 
               _expression.GetProperty(), 
               _expression.GetProperty().Name, 
               /* This works! */wrapper);
    return this;
}

I love it when there is a simple and elegant solution to a seemingly complex and nasty problem. :)

Tags: