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automatic code generation slides

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# Automatic Code Generation
----
## Plan
- Introduction<!-- .element: class="fragment highlight-blue" -->
- Approaches
- Xtend
- Acceleo
- Conclusion
----
## Code Generation
- Operation that generates textual artifacts (documents, source code, configuration, etc.) from models (graph-like).
- Motivation:
- **Abstraction**: from abstract syntax to the concrete syntax (textual)
- **Readability**: the models we generate are often not easy to read
- **Executability and testing**: easy to generate running code and test it
----
<!-- .slide: style="text-align: left;"> -->
```java
public class Team {
// (..)
}
public class Match {
// (..)
}
public class Player {
// (..)
}
```
<!-- .element: style="position:absolute; width:48%; right:0px;"-->
![](resources/png/uml-soccer.png)
<!-- .element: style="position:absolute; width:48%; left:0px;" -->
----
## Underlying model
- Set of classes of a specific programming language allowing to instantiate a model.
- For instance, to represent a UML model in Java, we need different classes:
- `UMLClass`
- `UMLAttribute`
- `UMLOperation`
- etc.
- The underlying model can be:
- generic or specific to a modeling language.
- follow a standard: JMI (Java Metadata Interface), EMF (Eclipse Modeling Framework).
----
## Plan
- Introduction
- Approaches<!-- .element: class="fragment highlight-blue" -->
- Xtend
- Acceleo
- Conclusion
----
## Code Generation Approaches
1. Script Languages
1. General Purpose Languages (GPLs): Java, C#
1. Generic transformation tools: Graph transformations, XSLT
1. CASE tools scripting languages: Objecteering, Rose
1. Dedicated model transformation languages: ATL, Operational QVT
1. Dedicated model to text transformation languages: xTend, Jet, Acceleo
----
## Script Languages
- sed (Stream Editor), 1973
- Awk (Text processing language), 1977
- Perl, 1987
- Python, Ruby, etc.
----
## Script example
```sh
#!/usr/local/bin/tcsh -f
# $* : Eiffel files to process
foreach f ( $* )
set classname = `basename $f .e`
echo -n "Doing $classname. "
set newcode = /tmp/inserted_text$$
############################################################################"
# First, extract attribute and association declarations
############################################################################"
sed -n -e '1,/^ * -- attribute/d' \
-e '/^ * -- associations/,$d' \
-e '/^ *[a-z][_A-Za-z0-9]* *: *[A-Z][_A-Z [\]]*[^a-z]*$/s/ *: */ /p'\
$f > /tmp/att_list$$
sed -n -e '1,/^ * -- associations/d' \
-e '/^feature/,$d' \
-e '/^ *[a-z][_A-Za-z0-9]* *: *[A-Z][_A-Z [\]]*[^a-z]*$/s/ *: */ /p'\
$f > /tmp/association_list$$
```
----
## General Purpose Languages
- Java, VB, C++, C#,... Your favorite language!
- Rules and scheduling implemented from scratch using the programming language
- No overhead to learn a new language
- Tool support to write the transformations
----
## GPL Approaches (1/2)
- Visitor-Based Approaches:
- Some visitor mechanisms to traverse the internal representation of a model and write code to a text stream
- Iterators, sequence of `Write()` calls.
----
## Visitor Example
- For example, you want to perform some processing on UML classes and their attributes.
- In the underlying model, a class and its associated attributes is represented by the composition relation below:
![](resources/png/class-attribute.png)
----
- Several visitors can be used to traverse the model:
![](resources/png/codegen-visitor.png)
----
- To see how the traversal completes its task, we will refer to the following sequence diagram:
![](resources/png/sd-visitor.png)
----
## Visitor Drawbacks
- Not scalable: a lot of code to write, difficult to maintain
- Basic behavior implementation: load the model, save the text, implement the methods that perform the code generation operation, etc.
- Lack of declarative query language
- Difficult to generate readable code (pretty printing)
----
## GPL Approaches (2/2)
- Template-Based Approaches
- A template consists of the target text containing slices of meta-code to access information from the source and to perform text selection and iterative expansion
- The structure of a template resembles closely the text to be generated
- Textual templates are independent of the target language and simplify the generation of any textual artifacts
----
## Templates
![](resources/png/template-engine.png)
<!-- .element: style="width:90%;" -->
----
## Template example
From:
```
class <<class.name>> {
<<FOR Feature f: class.features>>
private <<f.type f.name>> ;
<<ENDFOR>>
}
```
To:
```java
class Person {
private int age;
}
```
----
## Generic transformation tools
- Typically XML based
- But XML (XMI) is verbose
- XSLT can be used to transform XML trees into other (XML) (trees)
- But models are graphs
- Associations (reference) between nodes are done by values
- XSLT transformations are not really easy to maintain
- Better for simple transformations
----
## XSLT example
```xml
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:func="http://exslt.org/functions" xmlns:my="urn:my-functions" xmlns:date="http://exslt.org/dates-and-times" xmlns:math="http://exslt.org/math" extension-element-prefixes="func date">
<xsl:param name="p1"/>
<xsl:param name="p2"/>
<xsl:param name="p3"/>
<xsl:param name="p4"/>
<xsl:template match="/">
<root>
<function><xsl:value-of select="my:func()"/></function>
<date><xsl:value-of select="date:date()"/></date>
<max><xsl:value-of select="math:max(//max/value)"/></max>
<params>
<p1><xsl:value-of select="$p1"/></p1>
<p2><xsl:value-of select="$p2"/></p2>
<p3><xsl:value-of select="$p3"/></p3>
<p4><xsl:value-of select="$p4"/></p4>
</params>
</root>
</xsl:template>
<func:function name="my:func">
<func:result select="'func-result'"/>
</func:function>
</xsl:stylesheet>
```
----
## CASE tools scripting languages
- Arcstyler from Interactive Objects
- MDA-Cartridge, JPython (Python & Java)
- Objecteering from Objecteering Software
- J language
- OptimalJ from Compuware
- TPL language
- Fujaba (From UML to Java and Back Again)
- Open Source
----
## CASE tools scripting languages
- **Advantages**
- Good level of maturity
- Excellent integration with their CASE tool
- **Drawbacks**
- Proprietary languages and/or tight coupling with the CASE
- Often developed as a second thought, not central
- Many limitations when model transformation get complex
- Structuring, modularity, reuse problem
- Configuration management issue when they need to be evolved and maintained for long periods
----
## Dedicated model transformation languages
- Simplify development and maintenance of model-transformations
- Higher expression power
- Enhanced structuring
- Composition of rules
- Interoperability
----
![](resources/png/m2m.png)
----
## Transformation rule example
```
rule Member2Female {
from
s: Families!Member (s.isFemale())
to
t: Persons!Female (
fullName <- s.firstName + ' ' + s.familyName
)
}
```
----
## Model transformation drawbacks
- Transformation languages are generally used to implement model transformations
- Not really adapted to generate code
- Transformation rules tend to be granular
----
## Dedicated model to text transformation languages
- Acceleo
- Implementation reference for OMG's MTL (MOF Model to Text Transformation Language)
- Dedicated template engine for code generation
- Xtend
- Java + Templates + Sugar
----
## M2T Transformation Languages
- **Advantages**
- Template-based approach: text fragments + template expressions (constructs)
- Declarative query language: OCL, XPath, etc.
- Template engine: replaces template expressions with data at runtime and produces output files
- Scalable: at least more than other approaches
- Produces readable code
- **Drawbacks**
- Another language to learn
- Difficult to choose where to place specific behavior: in the meta-model or in the templates.
----
## Plan
- Introduction
- Approaches
- Xtend<!-- .element: class="fragment highlight-blue" -->
- Acceleo
- Conclusion
----
## Xtend
- Extension of Xpand (i.e. a template-based M2T)
- Brings together the advantages of GPLs and Template expressions
- Statically-typed PL which translates to comprehensible Java code, but improves:
- Lambda expressions
- Method dispatch & method extension
- Template expressions
- Generates reusable Java code
----
## Lambda expresssions
Java code:
```java
final JTextField textField = new JTextField();
textField.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
textField.setText("Something happened!");
}
});
```
Xtend code:
```java
textField.addActionListener([ e |
textField.text = "The command '" + e.actionCommand + "' happened!"
])
```
----
## Template expressions in Xtend
```java
def genCore (Calendar c) '''
private static Calendar buildCalendar() {
//creating a calendar
Calendar calendar = new Calendar();
//creating events
«FOR e : c.events»
Event event«c.events.indexOf(e)» = new Event();
event«c.events.indexOf(e)».setName("«e.name»");
event«c.events.indexOf(e)».setDate(«e.time.split('/').get(0)», «e.time.split('/').get(1)», «e.time.split('/').get(2)»);
event«c.events.indexOf(e)».setStartTime("«e.from»");
event«c.events.indexOf(e)».setEndTime("«e.to»");
event«c.events.indexOf(e)».setLocation("«e.location»");
calendar.addEvent(event«c.events.indexOf(e)»);
«ENDFOR»
System.out.println(calendar);
return calendar;
}
'''
```
----
## Example of Java generated code
```java
public CharSequence genCore(final Calendar c) {
StringConcatenation _builder = new StringConcatenation();
_builder.append("private static Calendar buildCalendar() {");
_builder.newLine();
_builder.append("\t\t");
_builder.append("//creating a calendar");
_builder.newLine();
_builder.append("\t\t");
_builder.append("Calendar calendar = new Calendar();");
_builder.newLine();
_builder.append("\t\t");
_builder.append("//creating events");
_builder.newLine();
{
EList<Event> _events = c.getEvents();
for(final Event e : _events) {
_builder.append("\t\t");
_builder.append("Event event");
EList<Event> _events_1 = c.getEvents();
int _indexOf = _events_1.indexOf(e);
_builder.append(_indexOf, "\t\t");
_builder.append(" = new Event();");
_builder.newLineIfNotEmpty();
_builder.append("\t\t");
_builder.append("event");
EList<Event> _events_2 = c.getEvents();
```
----
## Conditions
<<IF>>…<<ELSE>>…<<ENDIF>>
```java
def someHTML(Paragraph p) '''
<html>
<body>
«IF p.headLine != null»
<h1>«p.headline»</h1>
«ENDIF»
<p>
«p.text»
</p>
</body>
</html>
'''
```
----
## Loops
<<FOR>> … <<ENDFOR>>
```java
def someHTML(List<Paragraph> paragraphs) '''
<html>
<body>
«FOR p : paragraphs»
«IF p.headLine != null»
<h1>«p.headline»</h1>
«ENDIF»
<p>
«p.text»
</p>
«ENDFOR»
</body>
</html>
'''
```
----
## Loops with separators
```java
def someHTML(List<Paragraph> paragraphs) '''
<html>
<body>
«FOR p : paragraphs BEFORE '<div>' SEPARATOR '</div><div>' AFTER '</div>'»
«IF p.headLine != null»
<h1>«p.headline»</h1>
«ENDIF»
<p>
«p.text»
</p>
«ENDFOR»
</body>
</html>
'''
```
----
## Plan
- Introduction
- Approaches
- Xtend
- Acceleo<!-- .element: class="fragment highlight-blue" -->
- Conclusion
----
## Acceleo
- Reference implementation of the OMG «Model to Text Transformation Language» Standard
- Developed by Obeo
- Available in Eclipse (Eclipse Modeling Distribution)
- Combines an expressive query language with a template engine
----
## Modules
- Acceleo is organized in modules (`.mtl` files)
- Modules contain a file description, templates, and queries.
- The main template is annotated with `@main`
----
## Module structure
```
[comment encoding = UTF-8 /]
[**
* The documentation of the module generate2.
*/]
[module generate('http:///uml.ecore')]
[**
* The documentation of the template generateElement. * @param aDocument
*/]
[template public generateClass(c : Class)]
[comment @main/]
[file (c.name, false, 'UTF-8')]
[/file]
[/template]
```
----
- A module is identified by a name and a modeling language identifier (URI):
```
[module generate('http:///uml.ecore')]
```
- Template statements are specified inside tags `[.../]`:
- Field access: `[c.name]`
- Method call: `[c.getAbsolutePath()]`
----
## Conditions
- Syntax: `[IF]...[ELSE]...[/IF]`
```
[if (condition)]
(...)
[elseif (condition)]
(...)
[elseif (condition)]
(...)
[/if]
```
----
## Loops
```
[template public classToJava(c : Class)]
class [c.name/] {
// Attribute declarations
[for(a : Attribute | c.attribute)]
[a.type.name/] [a.name/];
[/for]
}
[/template]
```
----
## Calling other templates
```
[template public classToJava(c : Class)]
class [c.name/] {
// Attribute declarations
generateAttributes(c)
}
[/template]
[template public generateAttributes(c : Class)]
(..)
[/template]
```
----
## Queries
```
[query public hasStereotype( e : uml::Element, value: String) : Boolean =
e.getAppliedStereotypes()->select(e: uml::Stereotype | e.name = value)->notEmpty()
/]
```
----
## Plan
- Introduction
- Approaches
- Xtend