Hi, Have created an expression rule "increment" with one ru

vbhardwaj

Certified Senior Developer

over 8 years ago

Hi,

Have created an expression rule "increment" with one rule input "x", has the following definition :

with(
ri!x:ri!x + 1,
ri!x
)

I call this rule from another expression rule ::

with(
local!a:rule!increment(x:ri!y),
local!a
)

returns 11 if value of ri!y is 10, works fine.

But if I use the following code:

with(
local!a:rule!increment(x:ri!y),
ri!y
)

returns 10 if value of ri!y is 10.

I have two queries here :

1. Are rule inputs to expression rules Passed By Reference or Value ?
2. How can I design a rule which can return multiple values ?

Discussion posts and replies are publicly visible

0 vbhardwaj
Certified Senior Developer
over 8 years ago

rule!increment
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0 Rahul Gundu over 8 years ago

Answer for question 1:
As per documentation, Rule inputs are used to pass data into the expression rule. (Pass by variable) approach.
To answer your 2nd question,
If you want to apply same logic for multiple inputs use apply function which will return any type array.
Otherwise, use {} and define the logic in side {}.
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0 rawich over 8 years ago

@vikrantb, this is a tricky one, but also a common mistake trying to update rule inputs using with() or load() function. By defining this:

with(
ri!x:ri!x + 1,
ri!x
)

You actually created a local variable called ri!x, with value of rule input x + 1. Then you returned value of that local variable. No update made to the rule input.

We've seen this "pass by reference" magic works in SAIL expressions, but note that all the changes made to rule inputs are done in "Saving Phase" of SAIL evaluation. You can update rule inputs within saveInto of SAIL components.
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0 sikhivahans over 8 years ago

@vikrantb As specified above, the rule inputs are just meant for passing data might not hold valid always. As said by @rawichp they can be passed by reference especially in SAIL interfaces and because of this kind of mechanism only, we are able to update the rule inputs (which holds the reference of ACPs) in a component nested in a interface at any level.
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0 vbhardwaj
Certified Senior Developer
over 8 years ago

Thanks all. Understood the concept.
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