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

[Pablo Nussembaum]

Mark,
Probably I over simplification thing, but It's not possible to translate it to:
Object fact = getFact(var)
Method method = fact.getClass().getMethod("setName", new Class[] {param1.getClass(), .., paramN.getClass()});
method.invoke(fatc, parm1, .., paramN);

-- Bauna

On 04/07/2011 02:14 AM, Mark Proctor wrote:
> 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
>
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