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Magritte 3
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Magritte: Describe once,
get everywhere
• Introspection • Object persistency
• Reﬂection
• Object indexing
• Documentation
• Object setup
• Viewer building
• Object veriﬁcation
• Form/Editor building
• Object adaption
• Report building

• Data validation • Object customization

• Query processing • and much more

Why Magritte 3 All in all the "new" Magritte would look like in the following
From: Lukas Renggli example. Imagine a shop item with the accessor #place:

November 2010 Item>>place
^ place
I wrote a proposal this summer of want to proceed on Item>>place: aString
that, but of course I had to finish my writing and never actually place := aString
found the time to implement it:
The meta-description is defined on the instance-side and annotated. It
-------------------- can refer to itself for the possible places:
I propose to perform the following (non-backward compatible) changes Item>>placeDescription
in the Magritte 2 code-base to resolve some major annoyances and <magritte>
issues that keep on reoccurring:
^ MASingleOptionDescription new
- Move descriptions from class-side to instance-side. This resolves options: self possiblePlaces;
various issues such as cache-invalidation, instance specific label: 'Place of Item';
descriptions, dynamic descriptions, context dependent descriptions, accessor: #place;
etc. Furthermore the descriptions will be closer to the code they yourself
describe and it will be possible to describe class- and instance-side
of an object, not just the instance-side. Class extensions can modify a description using:
- Rename the method #description as the default entry point into Item>>placeDescriptionXmlStorage: aDescription
Magritte to #magritteDescription. This avoids common problems where <magritte: #placeDescription>
the domain model already defines such a method.
^ placeDescription xmlTag: 'xname'
- Instead of using a naming convention for description methods, use a
pragma called <magritte> to annotate the methods. And to extend and Since these changes are not backward compatible I'll try to provide
change existing descriptions use <magritte: aSelector>. Finally all automatic refactorings for most parts. Moving existing code to the new
Smalltalk implementation reached a consensus of pragmas that can be codebase will certainly cause some problems, but in the long run I
safely used cross-platform. believe this to be a much better approach than the current one. If
people have any feedback, concerns or other changes that would be
important in the same run I am happy to hear them.

Issues with Magritte2
• Name collision with #description
• class-side description:
• Cache-invalidation

• dynamic descriptions

• instance speciﬁc descriptions

• context dependent descriptions

Magritte 3
Descriptions move from class to instance.

Magritte 3
Use <magritteDescription> pragmas
rather than naming convention.

Magritte 3
All descriptions are dynamically generated.

Magritte 3
Rename #description to
#magritteDescription

Magritte 3
Rename #description to
Non-backward compatible

Magritte 2 Magritte 3

#description #magritteDescription

class-side descriptions instance-side description

#descriptionXXX <magritteDescription>

#magritteDynamicObject Not required

#descriptionContainer <magritteContainer>

Refactoring support
Gofer it
squeaksource: 'MetacelloRepository';
package: 'ConfigurationOfMagritte3';
load.

ConfigurationOfMagritte3 project stableVersion load:'Tools'

MMAttendee class>>#descriptionBookingDate
^ MADateDescription new
priority: 30;
label: 'Booking date';
tooltip: 'When the attendee booked';
accessor: #bookingDate;
default: [ Date today ] magritteDynamicObject;
yourself

priority: 30;
yourself

MMAttendee>>#descriptionBookingDate

priority: 30;
yourself

priority: 30;
yourself

<magritteDescription>
priority: 30;
yourself

priority: 30;
yourself

<magritteDescription>
priority: 30;
default: Date today;
yourself

Refactoring
Move class-side descriptions to instance-
side
add <magritteDescription>
Works for description extensions.
Operates at a method, class or package
level
Battle-tested in translating Pier

Refactoring will not
remove empty class-side categories
convert class-side message sends within
descriptions to add class
convert calls from #description to

Simplify Magritte 1 or 2 dynamic description work-
arounds
Remove #magritteDynamicObject and it’s associated
block

Porting guidelines
1. Use the refactoring support to move class-side
descriptions to instance side descriptions with pragmas -
making sure that any accessors to class side methods are
either preﬁxed with ‘class’ or moved to the instance side.
2. remove #magritteDynamic and remove the block around
the method.
3. search for all senders and implementors of #description
in your code, if they are magritte descriptions rename the
selector from #description to #magritteDescription
4. Remove any empty categories on the class side.

Status
All tests green.
Although the API changes appear significant the code
changes within Magritte are less significant and mainly
localised to MAPragmaBuilder
Pier has been ported to Magritte 3 (Pier 3) and is stable.
Magritte-Json and Magritte-XMLBinding ported
Other Magritte add-ons such Magritte-JQuery un-ported
No performance testing - descriptions are no longer
cached. Is this significant in the context of an application?

Next steps
• Install:
Gofer it
package: 'ConfigurationOfMagritte3';
load.

ConfigurationOfMagritte3 project stableVersion load:'Seaside'.

Gofer it
package: 'ConfigurationOfMagritte3AddOns';
load.

ConfigurationOfMagritte3 project stableVersion load.

• Use the refactoring tools to move to Magritte 3.
• Proﬁle performance within your application.

Load Sample

Gofer it
url: 'http://ss3.gemstone.com/ss/MagritteMagic';
package: 'ConfigurationOfMagritteMagic';
load.

(Smalltalk at: #ConfigurationOfMagritteMagic) load.

Further information

• Seaside Book:
http://book.seaside.st/book/advanced/magritte

• Lukas's site:
http://www.lukas-renggli.ch/smalltalk/magritte

• Magritte/Pier mail list:
<smallwiki@iam.unibe.ch>

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