[rules-users] Difference between adding $ at the beginning of a variable

[Mark Proctor]

It mostly helps  to differentiate bindings from fields
Person( name : name )
Person( name == name )

This is generally more readable.
Person( $name : name )
Person( name == $name )

That said I prefer to only bind patterns, and if the class name does not conflict with any field names, then I don't use $
p : Person()
Person( name == p.name )

AI systems traditionally use ? to differentiate variables, but that symbol is not allowed as a variable name char in java.

Mark
On 15 Jan 2013, at 20:10, Michael Anstis <michael.anstis at gmail.com> wrote:

> No difference, it was/is just used a lot in examples and advice given on here so has sort of become an unofficial standard.
> 
> Some argue the presence of "$" helps identify bindings when scanning DRL.
> 
> On 15 January 2013 20:04, suddeb <sudipta.deb at gmail.com> wrote:
> Hi,
> As I am very new to Drools, could you please tell me what is the difference
> between adding a $ at the beginning of a variable and without $.
> For example:
> rule "validate holiday"
> when
>    *$h1 : Holiday( `when` == "july" )*
> then
>    ......
> end
> 
> and
> 
> rule "validate holiday"
> when
>    *h1 : Holiday( `when` == "july" )*
> then
>    ......
> end
> 
> Regards,
> Sudipta Deb
> 
> 
> 
> --
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