I have finished removing Lua from Kaffeeklatsch and have enhanced Affe with the ability to bind field, property, and method calls at runtime. I noticed this gap when rewriting some of the key binding scripts; where I could just set a field before, my compiler threw an exception since it could not find the field on the IEffect interface. After wrestling with this for a while I finally came up with another hackish solution: a new operator.
The period operator binds during compilation, and the new dollar sign operator binds during runtime. Instead of the standard target-arguments-call emission, it emits a call to a static method declared inside Affe that takes the target object, the member name, and an object containing the call parameters. This method performs logic similar to a compiler-bound call (in fact, basically identical logic) except using the target's runtime type. One annoying pitfall of this technique is that since the return type cannot be known at compile time, a late-bound invoke necessarily returns an object. And, of course, to unbox a primitive you must perform an exact cast.
Since I didn't unbox automatically I added a parenthetical cast operator to Affe so that late-bound return values can be unboxed or converted. (Note that boxing is automatic.)
So where something like
Effect("fountain").Rotate = true; would make
Affe choke, this can now be written as
Effect("fountain")$Rotate = true;.
I am toying with the idea of flagging certain types to be intelligently bound. For example, if IEffect was so flagged, the compiler would try resolving the call and if it could not bind it, would convert the expression to a late-bound call. This would give all the speed of compile-time binding where possible, and fall back on runtime binding when that failed. Since I'm trying to make Affe basically a fast scripting language for .NET, this is optimal. It may make debugging harder since errors are not caught at compile time, but you'd have that problem with the $ operator anyway.