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No such thing as a small change

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Well ... some general thoughts on splitting up unknown code

Incremental strategy
  • create your test suite first
  • do little steps, and always test the result
  • use a revision control system like git
  • commit every change
  • use branches for experiments
  • once you found a previously untested bug expand your test suite and roll back


Study and understand

==== Perl essentials

  • strict and warnings
  • my vs our variables,
  • namespaces, scoping, blocks
  • exporter
  • constants
  • warn and die

==== Tools and techniques

==== your application

  • your data model ( database, configs)
  • input and output
  • avaliable doc
  • stakeholders (users, contributers, maintainers) to ask

  • analyze the dependencies of your subs (x calls y calls z)
  • analyze the shared variables
  • try to visualize the dependencies in a graph
  • the hierarchy should help identifying logical units (aka modules)
  • use tools to help you analyze like B::Xref
  • other tools like mentioned here: Searching for duplication in legacy code
  • identify dead code (never called subs, out-commented trash)
  • once you understood a mechanism, write it down
  • use Pod headers when possible
  • normalize (beautify) your code with Perl::Tidy
  • review your pod2html from time to time and fill gaps

Modularisation / Namespaces ?
  • bundle subs into modules by functionality not technology (not all sql in one module, eg look at the TABLE names )
  • require into the same namespace might be an easier intermediate step before learning to use exporter
  • modules normally require namespaces (packages)
  • package variables in other modules need to be fully qualified when used outside $Pkg::var
  • same for Pkg::subs()
  • modules allow to export vars and subs when use d
  • modules allow to pass and init shared variables when using import (like a database handle)

Object Oriented Programming

  • logical modules are sometimes better OO classes
  • check guides on "when OOP is better"
  • indicator: if you have to pass around same arguments
  • indicator: group of subs access always same global vars
  • indicator: init() routines for globals are sometimes better ->new()
  • easier to construct an object with encapsulated instance vars and class vars
  • have a look at Moo before doing old style OOP
  • make your code more fault tolerant
  • add argument checking to your subs
  • rewrite many positional args into named args
  • condense duplicated code into new functions
  • limit the scope of vars and subs if possible
  • give identifiers like variables meaningful names
  • document your strategy for future maintainers

See Also

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice


Expanded the OOP part

) that's an intermediate step exporting and importing is much cleaner

) As a rule of thumb from easier to better

  • require files same namespace (NB: my-lexicals can't be shared)
  • try to group connected subs into namespaces with package
  • use module different namespaces => full qualified identifiers for shared data
  • use module different namespaces => exporting and importing shared data
  • use oo-class : shared data in instance/class-vars and methods, transport via constructor and setter/getters

In reply to Re: Splitting program into modules by LanX
in thread Splitting program into modules by lis128

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