design pattern automation

@gfraiteur

a fresh view on design patterns, programming languages,

and agile methodologies

Design Pattern Automation

Gaël Fraiteur

PostSharp TechnologiesFounder & Principal Engineer

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Hello!

My name is GAEL.

No, I don’t thinkmy accent is funny.

my twitter

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My commitment to you:to seed a vision, not to sell a tool.

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The vision:Code at the right level of abstraction,with compiler-supported design patterns

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NotifyPropertyChanged,the wrong way

LAB 1

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1. A history of programming languages and patterns

2. Defining Design Pattern Automation

3. Pattern-Oriented Software Development

4. Tools for Design Pattern Automation

5. Agile Methodologies and Patterns

6. A last example

7. Q&A

8. Summary

Section

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Univac Assembly Language

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FORTRAN (1955)• 1955 - FORTRAN I

• Global Variables

• Arrays

• 1958 - FORTRAN II

• Procedural Programming(no recursion)

• Modules

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COBOL (1959)• Data Structures

• Natural Language

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LISP (1959)• Variable Scopes (Stack)

• Garbage Collection

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Simula (1967)• Classes as

abstraction mechanism

• Virtual procedures

• Object references

• Coroutines

Begin Class Glyph; Virtual: Procedure print Is Procedure print; Begin End;

Glyph Class Char (c); Character c; Begin Procedure print; OutChar(c); End;

Glyph Class Line (elements); Ref (Glyph) Array elements; Begin Procedure print; Begin Integer i; For i:= 1 Step 1 Until UpperBound (elements, 1) Do elements (i).print; OutImage; End; End;

Ref (Glyph) rg; Ref (Glyph) Array rgs (1 : 4);

! Main program; rgs (1):- New Char ('A'); rgs (2):- New Char ('b'); rgs (3):- New Char ('b'); rgs (4):- New Char ('a'); rg:- New Line (rgs); rg.print;End;

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Human Language

Cognition

Communication

Social Organization

Machine Language

Execution

Programming Languages

@gfraiteurHolašovice, Czech Republic

How is it possible that any simple farmer could make a house, a thousand times more beautiful than all the struggling architects of the last fifty years could do?

Christopher Alexander in The Timeless Way of Building, 1977

Pattern Thinking (1977)

Gael Fraiteur

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A world of patterns

LANGUAGE

REGULARITYRESOLUTION

OF FORCESSELF-

SUSTAINABILITY

VARIETY UBIQUITY

@gfraiteurLanguage Enables Cognition

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Language for the Trade

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Patterns as

WISDOM in canonical form

• Name

• Also Known As

• Problem

• Context

• Forces

• Example

• Solution

• Structure and Dynamics

• Implementation

• Example Resolved

• Known Uses

• Variants

• Consequences

• Relationships

• Name

• Also Known As

• Problem

• Context

• Forces

• Example

• Solution


• Implementation


• Known Uses

• Variants

• Consequences

• Relationships

• Name

• Also Known As

• Problem

• Context

• Forces

• Example

• Solution


• Implementation


• Known Uses

• Variants

• Consequences

• Relationships

• Name

• Also Known As

• Problem

• Context

• Forces

• Example

• Solution

• Description


• Known Uses

• Variants

• Consequences

• Relationships

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Software Patterns (1995)• Apply to OO design

• Canonic pattern description

• First catalogue of 23 patterns

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In 2013, eighteen years later, design patterns still live in their parent’s house – books.

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Latent Redundancy

Bad OO code Good OO code Ideal code

Intrinsic variability Latent redundancy Bad redundancy

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Cost of low abstraction• Boilerplate code

• More bugs

• Code review

• Changing the pattern implementation

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6. A last example

7. Q&A

8. Summary

Section

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Pattern Automation

Automation is the use of machines, control systems and information technologies to optimize productivity in the production of goods and delivery of services.

Wikipedia

Design Pattern Automation is the use of tools to optimize productivity in the implementation of software based on patterns.

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Pattern-Aware Compilers allow for coding at the level of abstraction of design patterns.

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Design Pattern Automation is new

© hellraiser

MYTH 1

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Pattern C# Keyword

Dispose using

Lock lock

Publish-Subscribe event

C# implements several patternsTRUTH 1

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But C# does not let you implement your own patterns.

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code generators were proved wrong

You can’t automate patterns because…

MYTH 2

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pattern-aware programming languages and compilers

we don’t need code generators but

TRUTH 2

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there are too many skills involved


MYTH 3

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industrial revolutionSkill scarcity motivated the

TRUTH 3

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Our own industrial revolution:

Making it easier to build good software

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6. A last example

7. Q&A

8. Summary

Section

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they are way too complex general abstract


MYTH 4

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a normal part of any engineering process

Making abstract things concrete is

TRUTH 4

ConcreteAbstract

Automatable

Non-Automatable

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Pattern-Oriented Implementation Process

Architecture Pattern

• Defines Subsystems

Design Pattern

• Define Components

• General problem• Language-

independent

Implementation Pattern

• Defines source artefacts

• Language-specific

• Framework-specific

• Application-specific

• Implementation guidelines

Source code

• Executable

High Abstraction Zero Abstraction

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Example: Observer Pattern

1. Vanilla Design Pattern (GoF)

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1

2

3Call OnPropertyChanged whenever a property has changed.

2. Language-Specific Pattern (C#)

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• Analyze property-field dependencies

• Modify all non-const methods

• Whenever a relevant field has changed

• When invariants are valid (after all changes in the object have been done)


When? How?

3. Application-Specific Pattern (C#)

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Example: Observer Pattern4. Source code

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NotifyPropertyChangedwith PostSharp

LAB 2

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6. A last example

7. Q&A

8. Summary

Section

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Transformation

Verification

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Pattern Automation Technologies

Pattern Automati

on

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Example:

Richman’s Singleton• Static validation rules:

• A single constructor

• Constructor never called

• Code transformation:

• Introduce static field

• Introduce static method GetInstance

• Make constructor private

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[Nemerle.MacroUsage (Nemerle.MacroPhase.BeforeInheritance, Nemerle.MacroTargets.Class)] macro Singleton (t : TypeBuilder) { def mems = t.GetParsedMembers();

// find constructor, which we will need to call to create instance def ctor = mems.Filter(fun (x) { | <[ decl: ..$_ this (..$_) $_ ]> => true | _ => false });

match (ctor) { | [ <[ decl: ..$_ this (..$parms) $_ ]> as constructor ] => {

// we must prepare expressions for invoking constructor def invoke_parms = parms.Map(x => <[ $(x.ParsedName : name) ]>); // first define the field, where a single instance will be stored t.Define(<[ decl: private static mutable instance : $(t.ParsedName : name); ]>);

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// finally, define getter t.Define (<[ decl: public static Instance : $(t.ParsedName : name) { get { // lazy initialization in generated code when (instance == null) instance = $(t.ParsedName : name) (..$invoke_parms); instance; } } ]>);

// make sure constructor is protected constructor.Attributes |= NemerleAttributes.Protected; | _ => Message.Error ("Singleton design pattern requires exactly one constructor defined") } }

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[Singleton]class LoadBalancer{ // Details omitted}

public class SingletonApp{ public static Main() : void { def b1 = LoadBalancer.Instance; def b2 = LoadBalancer.Instance; // Same instance? when ((b1 : object == b2) && (b2 : object == b3) && (b3 : object == b4)) Console.WriteLine( "Same instance" ); // Do the load balancing Console.WriteLine( b1.Server ); Console.WriteLine( b2.Server ); }}

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Macro-enabled .NET languages• Nemerle

• Scala

• Boo

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Poorman’s Pattern

Automation: Static Analysis

Pattern Automati

on

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Example:

Poorman’s Singleton• Static validation rules:

• Static private readonly field named ‘singleton’, whose type is the current type.

• Static public method GetInstance() whose return type is the current type, returns field ‘singleton’.

• Class constructors are private.

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Singleton with Architecture Unit Tests

LAB 3

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• Limitations

• Inadequate UI and error reporting

• Limited reflection API

• Alternatives

• FxCop

• PostSharp Architecture Framework

Architecture Unit Tests

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5. Agile Methodologiesand Patterns

6. A last example

7. Q&A

8. Summary

Section

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All design patterns are found in books

MYTH 5

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spinning into

Emergent Design

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Itera

tion 1

Itera

tion 2

Itera

tion 3

Itera

tion 4

Itera

tion 5

Itera

tion 6

Itera

tion 7

Itera

tion 8

Itera

tion 9

Itera

tion 10

Qualit

y

Eroding Design

Quality

Distance from design

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Itera

tion 1

Itera

tion 2

Itera

tion 3

Itera

tion 4

Itera

tion 5

Itera

tion 6

Itera

tion 7

Itera

tion 8

Itera

tion 9

Itera

tion 10

Qualit

y

Emergent Design

Quality

Knowledge

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Iterative Design

• Unit Tests• Load Tests• Integration

Tests

• Project• Team• Design

• Abstract• Design• Refactor• Implement

• Time• User Stories

Planning Development

TestingReview

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Agile & Continuous Improvement

Design

RefactorImplement new stuff

Learn

KnowledgePatternsLanguage

Requirements

Code

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We’re a part of a whole

Software EngineeringDiscipline

Company / Personal

Know-How

Project

EngineeringDiscipline

@gfraiteurHolašovice, Czech Republic

Patterns emerge naturally from iterative design processes.

TRUTH 5

Gael Fraiteur

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Example of application-specific pattern:

Business Rule Pattern

• For any class derived from BusinessRule:

• Name ends with “BusinessRule”

• No public constructor

• Has nested class named “Factory”

• Has parameterless public constructor

• Annotated with [Export(typeof(IBusinessRuleFactory))]

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6. A last example7. Q&A

8. Summary

Section

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Example:

Reader-Writer Synchronized Object

• Code Generation

• Introduce interface IReaderWriterSynchronized

• [ReaderLock], [WriterLock] executes the method with the right locking level

• Code Verification

• All fields must be private

• Cannot access field without proper lock

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ReaderWriterSynchronized with PostSharp

LAB 4

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Q&AGael [email protected]@gfraiteur

@gfraiteurCopyright © by Arild Vågen

Summary• Compilers must do more to raise abstraction

level

• Patterns stem from continuous improvement

BETTER SOFTWARE THROUGH SIMPLER CODE

design pattern automation

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