Living with The Legacy Code: A very Short Guide

Definition of Legacy Code: Code without tests. Code youve “inherited” Code noone understands. Technical debt Aim to understand the concepts and motivations. Get it into version control. Identify the inflection point. Create integration acceptance tests. Set up your continuous integration environment

Legacy Code

@rowan_m

Ibuildings Plusnet

What is

“Legacy Code”?

What is

“Legacy Code”?

Who has never created Legacy Code?

My own

story

little

Starting a project

Aim to understand

the concepts and motivations

Try using the application

Find and then read

any / all documentation

Talk to the original developers

Talk to the users

… especially the

“different” ones

the code

Catalogue the live platform

& environment

Recreate it!

Deploy the code

Time to enter

The Code

Reading Static analysis

Dynamic analysis

Time to enter

The Code

ph pd

oc

phpdoc -ti 'Sweet Application' \ -pp -o HTML:Smarty:PHP \ -d Libraries \

-t Docs

http://www.phpdoc.org/

Title

Style Code in here

Docs out here!

Beware of type-hiding!

Type-hinting

Type-hiding

/**

* @param array $opts Current options

* @return array Options with flag set

*/

function setFlag( array $ opts ) {

$ opts ['flag'] = true ;

return $ opts ;

}

/**

* @param int $fullPence Full price in pence

* @return float Discounted price in pence

*/

function applyDiscount( $ fullPence ) {

return ( $ fullPence * 0.8 ) ;

}

do xy

ge n

http://www.stack.nl/~dimitri/doxygen/

doxygen -s -g ~/doxy.conf vim ~/doxy.conf

# edit at least this OUPUT_DIRECTORY

# play with the rest

cd ~/dev/project doxygen ~/doxy.conf Docs out here Code in here

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17 | WARNING | Line exceeds 80 characters; contains 87 characters

32 | WARNING | Line exceeds 80 characters; contains 87 characters

36 | ERROR | Opening class brace must be on a line by itself

36 | ERROR | Closing brace must be on a line by itself

-http://matrix.squiz.net/developer/tools/php_cs

Cont inuo

us Inte grat

ion

http://www.phpundercontrol.org/

http://hudson-ci.org/

n time!

t, te st

Ignore it, code anyway

Ignore it, code anyway

Please don't.

Ignore it, code anyway

Please don't.

however

Deadlines, clients,

money, etc.

Deadlines, clients,

money, etc.

Secure a follow-up project

Make everyone

aware of the risks

Why do you need the code?

Why do you need the code?

Library dependency Adding new behaviour Changing behaviour

simple

complex

Isolate legacy dependencies

Isolate legacy dependencies

Create an anti-corruption layer

Complete isolation

Create a legacy service

Partial isolation

Wrapper classes

or methods

function extract_brain( & $ person ) {

$ brain = $ person [' brain '];

unset( $ person [' brain ']);

return $ brain ; }

/**

* @param array $person

* @return bool living or not

*/

function create_life( $ person ) {

require_once( LIB_DIR ' /nuts_n_bolts.inc ');

:(

Wrapper class

public function extractBrain(Person $ p ) {

// format to legacy style

$ pLgcy = $this -> toArray( $ p ) ;

// run legacy code

$ bLgy = extract_brain( $ pLgcy ) ;

// format to new style

$ p = $this -> toPerson( $ pLgcy ) ;

$ b = $this ->t oBrain( $ bLgcy ) ;

return array ( $ p , $ b ) ; }

public function createLife(Person $ p )

{

// validate

if ( $ person-> isAlive()) throw new LivingException() ;

// format to legacy style

$ pLgcy = $this -> toArray( $ p ) ;

// run legacy code

$ pLgy = create_life( $ pLgcy ) ;

// format to new style

return $this -> toPerson( $ pLgcy ) ; }

}

Some code you can use

:) Wrapper class

Changing the code

Changing the code

Take an incremental approach

Commit to 1 day

at a time

Difficult to estimate Hidden dependencies Unknown behaviour

1 Get it into

version control

2 Identify the inflection point

3 Create integration

& acceptance tests

4 Set up your continuous integration

environment

5 Rewrite and refactor!

of changes

Mixed Procedural →

includes HTML PHP

PHP

HTML HTML PHP

HTML HTML

HTML PHP

PHP PHP

HTML

PHP PHP HTML

HTML

includes HTML PHP

PHP

HTML HTML PHP

HTML HTML

HTML PHP

PHP PHP

HTML echo

if if

HTML

PHP PHP HTML

Procedural OO →

static method static method static method

static method

static method includes

static method static method static method

static method

static method

includes

method method method

method

constructor includes

Sprout method / class

public function createInvoice(Account $ acc , array $ charges )

The existing code

“We just need to be able to give

each client their own personal

discount on certain charges.”

public function createInvoice(Account $ acc , array $ charges )

$ accDisc = new AccountDiscounter( $ acc ) ;

$ discountedCharge = $ accDisc-> calculate( $ chg ) ;

return $ discountedCharge ;

}

The new code

public function createInvoice(Account $ acc , array $ charges )

{

$ invoice = new Invoice() ;

foreach ( $ charges as $ chg ) {

// Sprout new behaviour!

$ chg = $ this-> calcDiscount( $ acc , $ chg ) ;

$ invoice-> addLine( $ chg-> getDesc() , $ chg-> getAmount()) ; }

return $ invoice ;

}

private function calcDiscount(Account $ acc , Charge $ chg )

{

$ accDisc = new AccountDiscounter( $ acc ) ;

$ discountedCharge = $ accDisc-> calculate( $ chg ) ;

return $ discountedCharge ;

}

Call it

Untestable OO testable OO →

Dependency Inversion / Extraction

The Problem

public function calcDiscount(Account $ acc , Charge $ chg )

{

$ accDisc = new AccountDiscounter( $ acc ) ;

$ discountedCharge = $ accDisc-> calculate( $ chg ) ;

return $ discountedCharge ;

The Problem

public function calcDiscount(Account $ acc , Charge $ chg )

{

$ accDisc = new AccountDiscounter( $ acc ) ;

$ discountedCharge = $ accDisc-> calculate( $ chg ) ;

// contact the database

// call a web service

}

}

Quick Solution

public function calcDiscount(Account $ acc , Charge $ chg )

{

$ accDisc = $ this-> getAccountDiscounter( $ acc ) ;

$ discountedCharge = $ accDisc-> calculate( $ chg ) ;

Dependency Injection Solution

public function calcDiscount(Account $ acc , Charge $ chg )

{

$ accDisc = $ this-> discounter ;

$ discountedCharge = $ accDisc-> calculate( $ chg ) ;

(v2) Dependency Injection Solution →

public function calcDiscount(Account $ acc , Charge $ chg )

{

$ accDisc = $ this-> discounter ;

$ discountedCharge = $ accDisc-> calculate( $ chg ) ;

Any questions?

Feedback to: http://joind.in/1242

@rowan_m