C++- und Ruby- und ...Refactoring für Eclipse

iX-Konferenz Bessere Software! 2006

Prof. Peter SommerladHSR - Hochschule für Technik RapperswilInstitut for SoftwareOberseestraße 10, CH-8640 Rapperswilpeter.sommerlad@hsr.chhttp://ifs.hsr.chhttp://wiki.hsr.ch/PeterSommerlad

Bessere Software – Einfach, Schneller

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Assumptions/Questions

•Talk in English or deutsch?

•I assume that you ask questions when you have them. Please interrupt me.

•I assume that you are not yet very familiar with the concept of Refactoring

o short explanation is optional

•I assume that you are familiar with object technology and either C++, Ruby or Java

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Peter Sommerladpeter.sommerlad@hsr.ch

• Work Areaso Refactoring Tools (C++,Ruby,...)o Decremental Development

(make SW 10% its size!)o Modern Software Engineeringo Patterns

Pattern-oriented Software Architecture (POSA)

Security Patterns

• Backgroundo Diplom-Informatiker (Univ.

Frankfurt/M)o Siemens Corporate Research -

Municho itopia corporate information

technology, Zurich (Partner)o Professor for Software

HSR Rapperswil, Head Institute for Software

Credo:

• People create Softwareo communicationo feedbacko courage

• Experience through Practiceo programming is a tradeo Patterns encapsulate practical

experience

• Pragmatic Programmingo test-driven developmento automated development

• SimplicitySimplicityo fight complexity

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Overview

• Introduction to Refactoringo Elementary Refactorings (optional)

•Refactoring Pluginso typical approach

•C++ Refactoring Pluginso Why is it so hard?o Cerp Demo

•Ruby Refactoring Plugino What is easier?o "Demo"

•Outlooko future Refactoring features and languageso RadRails, C++, Python, PHP, groovy, PL/1, Ada, Cobol...?o Funding?

Introduction

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Refactoring

"Improving the Design of Existing Code" -- Martin Fowler

•after we learned to solve the programming problem, solve it in a better way.

•process:o smell "bad code"o then refactor ito run all (unit-) tests

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Improving Design

•improving means to eliminate violation of principles of good design, i.e.,o bad names – uncommuncative codeo duplication – DRY principle, OAOO, SPOTo lack of cohesion – too largeo bad dependencies – wrong direction or circular

•goalso understandable program codeo achieve conceptual integrityo simplicity – not simplistico testability (see iX conference 2005)

q3 foo

ClassA

ClassB

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Refactoring tools and Eclipse

•Java JDK provides a good support for refactoring automationo eases developmento refactoring possible without too many unit tests

•Eclipseo provides language independent framework for

refactoring toolso Development Toolkit plugins for many other

languages available

Most non-Java Toolkit plugins lack adequate Refactoring support

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Benefits and Drawbacks of automated Refactoring

•Fowler's book describes Refactoring as a manual process of (very) small stepso tedious workbut o makes programmers think on what to achieve

•automated Refactoringo less tedious, easier to undo, no/less automatic re-

testing requiredbuto lulls programmers, can refactor in circles without

code improvement, refactor without sense of good design, tools not perfect

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Some Important Refactorings (0)

•Renameo good names are importanto while we program, we learn better names for

fields, variables, classes, methods or functionso renaming benefits heavily from automatic

support find all places where this named program element is

used by tracking references from a definition no need to blindly change the name string everywhere no need for manual checking if name means something

else in another place better than sed –e 's/oldname/newname/g'

q3 circleDiameter

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Some Important Refactorings (1)

•Change Bidirectional Association with Unidirectionalo lower coupling, remove circular dependencyo no automation, requires thinking and planning

o other simpler refactorings support this (ie. Move)

C1

C2

C1

C2

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Some Important Refactorings (2)

•Extract Classo improve cohesiono smaller classes

C1

field1field2

m1()m2()

C1

field1

m1()

C2

field2

m2()

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Some Important Refactorings (3)

•Extract Methodo reuse codeo less duplication

C1

+m()

m() { before(); a(); b(); after();}

C1

+m()-extracted()

m() { before(); extracted(); after();}

extracted() { a(); b();}

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Some Important Refactorings (4)

•Move Fieldo better cohesion,

C1

C2

field

C1

field

C2

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Some Important Refactorings (5)

•Move Methodo move code where it belongs

C1

C2

m()

C1

m()

C2

Principles of Refactoring tools

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Principles workings of Refactoring tools

•based on abstract syntax trees ASTo internal representation of program code

generated by a parsero with name bindings (know what a symbol means)

aka symbol table

•automated Refactoring mechanics (in Eclipse)o check preconditions (correct selection)o ask for user input (e.g., new name)o modify ASTo re-generate source codeo check postconditionso visualize changeso perform changes

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Hard parts of automated Refactoring

•Commentso typical parsers ignore commentso comments are often not part of an AST

•Language redundancyo different syntax for same semanticso often identical AST representation

•Preserve semantics and compilabilityo moving elements can change meaningo moving code can break compiles

sequential nature of source code

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AST parsing Examplesimplified

a = check ? "ok" : "failed" # some check

a check "ok" "failed"

lvar str_literal str_literallvar

if_expr

condition then_part else_part

assignment

some check

comment

?

classic abstract syntax tree

comment-extended abstract syntax tree

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Creating Refactoring Plugin Infrastructure

•Tasks:o extend parser and AST to keep comments

JDT loses comments in some cases (or used to) C++ especially hard with preprocessor

o generate code from AST without losing comments pretty-printing in context, e.g., nesting levels might need to rely on original formatting

o automate tests for this have to deal with all syntax idiosynchracies

o understand name bindings for necessary semantic checks for individual refactorings can require extending AST

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Re-generate Code from AST

a check "ok" "failed"

lvar str_literal str_literallvar

if_expr

condition then_part else_part

assignment

some check

comment

a = check ? "ok" : "failed" # some checka = if check "ok" else "failed" end # some check

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Additional features

•(re-)generating source code from an extended AST allows additional features

•Pretty printingo configurable consistent layout of source code

•Code generationo generate typical source code pieces

i.e. generate getters/setters/accessors

o actually changing the code's semantics generate constructor using fields override method

Our Projects

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Our Refactoring projects

•CERP – simple C++ Refactoring

•Ruby Refactoring

•CDT – C++ Refactoring

•Python

•Rails

•PHP

•groovy

•your language here... (PL/1, ABAP, Cobol?)

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C++ Refactoring in Eclipse

•CDT provides support for C++ development in Eclipseo mainly supported by companies providing

development tools for embedded platformso Refactoring not in their focus (yet)o CDT's evolution provides some interesting and

duplicate design elements and features i.e. several parsers, several source representations

•C/C++ is especially hard to deal witho #includes, Macros, templateso hand-coded parsers – not grammar generatedo redundancy of definitions with declarations

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Example of C++ specific problems

•Preprocessoro #include

classical compiler physically includes

o comments already removed by preprocessor

o macros can do strange things to syntax in original source

•Separate compilation unitso .c, .cpp fileso package and project concept by convention or

separate tools

virtual Preprocessin

g

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Eclipse CDT specific challenges

•different generations of source code representation and corresponding parserso CModel - elementary information of position

of elements today deprecated

o DOM – the AST of a single translation unit "completely" parsed code representation

o PDOM – "persistent" DOM not yet complete (but almost now)

o Rename-Refactoring – own parser and "DOM" copy-paste reuse of DOM parser

•neither represents comments or all preprocessing information

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Demo CERP

•Diploma thesis by Guido Zgraggen and Christian Cavegno 8 weeks of intense work fall 2005

•uses CDT's legacy CModel to find pieces of code

•generates source code without relying on complete ASTo usable, but problems with some C++ syntax

• "interesting" C++ Refactoring: synchronize Methodo adjust Definition with Declaration or vice versa

•provideso Declare Method - generates method declaration from impl.o Extract Baseclass o Implement [from] Baseclasso Hide Method – make method privateo Implement Method – generated from declarationo Separate Class – moves a class' definition into separate fileo Synchronize Method [signature]

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CERP Menu

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Extract Baseclass Dialog

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Refactoring Preview Wizard

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Ruby RefactoringEasier...

•Ruby has a simpler syntaxo with some problems when re-arranging codeo parentheses are optional in some places but

required for disambiguating

•dynamic typing eases code generation and refactoringo everything is an object

•JRuby as parser needed adjustments

•RDT needed extension

•Rails team enthusiastic supporters

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Demo RDTFeatures

•Generate Accessors

•Generate Constructor using Fields

•Override Method

•Rename Local Variable

•Push Down Method

•Extract Method

•Extract Class

•Rename Class, Method, Field

• Inline Class, Method, Field

•Split Temporary Variable

•Move Method, Field

•Convert Local Variable to Field

•Merge Class' Parts from different Files

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Extract Method Refactoring

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Generate Accessors

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Inline Temporary

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Merge Class Parts

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Push Down

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Rename Local

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Split Temporary Variablewhen multiple assignments occur

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Create Field from Local

Conclusion and Outlook

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Difficulties of developing Refactoring plugins

•Unit Testingo workbench expensive to start

decouple your code and tests from workbench as good as possible

run tests as often as possible and as quick as possible

o many tests required write configurable tests files with test data, not code with test cases quick to add and extend tests

• "Fixing" and extending existing Plugins - Logisticso establish collaboration with plugin projectso de-couple from plugin projects

• frequent releases of Eclipse platform and projectso especially with volatile projects like CDT, hard to keep up

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Our Refactoring projects

•CERP – simple C++ Refactoring

•Ruby Refactoring

•CDT – C++ Refactoring

•Python

•Rails

•PHP

•groovy

•your language here... (PL/1, ABAP, Cobol?)

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Future Refactoring and Plugin projects @ IFS

• incorporate Ruby Refactoring into official RDT and RadRails projects

o RubyOnRails-specific Refactorings

•extend C++ CDT Refactoringo still much work to do, but basic infrastructure available:

comments aware parser and AST AST rewriting virtual preprocessing keeps original source

•Python Refactoringo current semester student project

•Projects, Plans and Ideas foro Quick-Fixes for FindBugsTM (Java)o groovy, PL/1(?), ABAP (?), Cobol(?), Ada(?) - Refactoringo Business-Process Refactoring

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Have fun Refactoring!

•Remember: Refactor to simplify your code

o or order specific Refactoring features for your organization

•Do not hesitate to contact me for further information and feedback:

o peter.sommerlad@hsr.ch

Online-Resources:

•http://ifs.hsr.ch

•http://ifs.hsr.ch/cerp/updatesite - CERP

•http://r2.ifsoftware.ch – Ruby Refactoring Plugin

Sponsoring welcome