Question

I’m generating compiled getter methods at runtime for a given member. Right now, my code just assumes that the result of the getter method is a string (worked good for testing). However, I’d like to make this work with a custom converter class I’ve written, see below, ‘ConverterBase’ reference that I’ve added.

I can’t figure out how to add the call to the converter class to my expression tree.

    public Func<U, string> GetGetter<U>(MemberInfo info)     {         Type t = null;         if (info is PropertyInfo)          {             t = ((PropertyInfo)info).PropertyType;         }         else if (info is FieldInfo)         {             t = ((FieldInfo)info).FieldType;         }         else         {             throw new Exception('Unknown member type');         }          //TODO, replace with ability to specify in custom attribute         ConverterBase typeConverter = new ConverterBase();          ParameterExpression target = Expression.Parameter(typeof(U), 'target');         MemberExpression memberAccess = Expression.MakeMemberAccess(target, info);          //TODO here, make the expression call 'typeConverter.FieldToString(fieldValue)'          LambdaExpression getter = Expression.Lambda(memberAccess, target);          return (Func<U, string>)getter.Compile();     } 

I’m looking for what to put in the second TODO area (I can handle the first :)).

The resulting compiled lambda should take an instance of type U as a param, call the specified member access function, then call the converter’s ‘FieldToString’ method with the result, and return the resulting string.

Answer 1

Can you illustrate what (if it was regular C#) you want the expression to evaluate? I can write the expression easily enough – I just don’t fully understand the question…

(edit re comment) – in that case, it’ll be something like:

    ConverterBase typeConverter = new ConverterBase();     var target = Expression.Parameter(typeof(U), 'target');     var getter = Expression.MakeMemberAccess(target, info);     var converter = Expression.Constant(typeConverter, typeof(ConverterBase));      return Expression.Lambda<Func<U, string>>(     Expression.Call(converter, typeof(ConverterBase).GetMethod('FieldToString'),         getter), target).Compile(); 

Or if the type refuses to bind, you’ll need to inject a cast/convert:

    MethodInfo method = typeof(ConverterBase).GetMethod('FieldToString');     return Expression.Lambda<Func<U, string>>(         Expression.Call(converter, method,             Expression.Convert(getter, method.GetParameters().Single().ParameterType)),             target).Compile();