[rules-dev] modify( expr ) {....}

[Mark Proctor]

I'm at the stage where I cannot make this work in a robust way when 
using the java dialect:
modify( getFact( var ) ) { setName("yoda") }

The problem is we have to infer the type of the expression. If the 
expression is complex using variables in methods, we get method 
ambiguity if we don't know all variable types. Once we have the 
expression type we rewrite this as:
Person obj = ( Person) getFact(var);
obj.setName( "yoda" );

Edson did this originally by using mvel to analyse the expression. The 
problem is that if the expression uses any local variables, we don't 
know what those are. So we need to analyse the entire consequence, we 
started to do this with MVEL but we have reached one too many stumbling 
blocks - most recent of those is MVEL does not understand java generics. 
I've put in about 3 weeks trying to solve this with mvel, and now had to 
stop. When MVEL adds generics we can hopefully resume this work again.

For now i'm having to roll back to our current behaviour. The positive 
news is that no one has reported issues with this. I'm guessing most 
people use just the fact instance, not expressions, and if they use an 
expression it's simple. So the brittleness is not showing up.

Anyway the work around for now is to explicitley cast, that should 
resolve the issue, if it comes up for anyone. I'm tempted to say that 
expressions are only officially supported when used with casting. 
Atleast until we can do robust type inference:
modify( (Person) getFact( var ) ) { setName("yoda") }

Mark