How action at a distance appears in software engineering - and why to avoid it like the plague!

1. Andrew Solomon London Perl Meetup #1 2018 @ Zoopla Version 1.0
Action
at a
distance
What’s that got to do with me?

2. Action at a distance
Gravitational Field

3. Action at a distance
Gravitational Field
Quantum Entanglement

4. Action at a distance
Gravitational Field
Quantum Entanglement
Mason Web Framework

5. Confidential Customized for Lorem Ipsum LLC Version 1.0
Summary
The goal
The data
The action
The code
The problem
Examples
The manifestations
The ultimatum

6. The Goal
I provide a url
I get content in return

7. The Data we give Mason
Green = has a handler

8. The Action Mason takes
Find the handler
descend(X,for-sale/edgeware-rd) , handler(X).

9. meta-Perl
implementation...

10. The data...
child(for-sale,for-sale/oxford).
child(for-sale,for-sale/london).
child(for-sale/london,for-sale/w10).
child(for-sale/w10,for-sale/edgeware-rd).
child(to-rent,to-rent/london).
handler(for-sale).
handler(for-sale/london).

11. … in Prolog
descend(X,Y) :- child(X,Y).
descend(X,Y) :- child(X,Z),
descend(Z,Y).

12. The problem
1
We determine the content of the page from
the url by database + logic

13. The problem
1
We determine the content of the page from
the url by database + logic
2
The same data is required for multiple
descendents of a Mason node

14. The problem
1
We determine the content of the page from
the url by database + logic
2
The same data is required for multiple
descendents of a Mason node
3
We wind up storing this data in global
variables as we traverse the Mason tree

15. The problem
1
We determine the content of the page from
the url by database + logic
2
The same data is required for multiple
descendents of a Mason node
3
We wind up storing this data in global
variables as we traverse the Mason tree
4
Data retrieved and munged in several non-
obvious places before arriving at the
template.

16. Action at a distance
The problem

17. Example - The Doppelganger of Ingleton
https://www.telegraph.co.uk/news/features/10905575/Britains-doppelganger-place-names.html

19. Manifestations

20. Mojo
Passing controller objects into the model

21. PSGI
Performing path modifications in outer
layers

22. Everywhere
Doing things outside the appropriate
context

23. Code reviewer
The Ultimatum
Just because you can...

24. Code reviewer
The Ultimatum
Just because you can…
Doesn’t mean you should.

25. Code reviewer
The Ultimatum
Just because you can…
Doesn’t mean you should.
End action at a distance

26. Raiden - Turning over a new leaf at Zoopla

27. Thank you.