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Initializing a class with a Dictionary

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sergio_101
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Initializing a class with a Dictionary

sergio_101

is it possible to initialize a class with a dictionary? my first thought would be to create a method like:

intializeWithDictionary: aDictionary

then, loop through the elements and do something like:

instVarNamed: key put: value

but the book says:

Caveat: Although these methods are useful for building development tools, using them to develop conventional applications is a bad idea: these reflective methods break the encapsulation boundary of your objects and can there- fore make your code much harder to understand and maintain.-- 

should i avoid this?
Clément Béra
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Re: Initializing a class with a Dictionary

Clément Béra
Hello,

I think you should look at the STON framework. STON looks like JSON for smalltalk objects. Basically it does the same as your idea but instead of a dictionary it loads fields of an objects from a STON file which looks like a JSON file (a STON is kind of an extended Dictionary exported as a string, but it has support for more that instance variables).

Now if you want to go your way, to me what you want to do looks fine. These methods can be used for development tools but also for frameworks and stuff like that. The thing to do it is to add this method in Object and add support so it can work on all objects in the system.

Object>>#intializeWithDictionary: aDictionary
    self class isVariable ifTrue: ["specific case ?"]
    self class isBytes ifTrue: ["specific case ?"]
    self class isCompiledMethod ifTrue: ["specific case ?"]
    self class isSmallInteger ifTrue: ["specific case"]
    aDictionary keysAndValuesDo: [ :key :value |
        self instVarNamed: key put: value ifAbsent: [ self error: 'no ', key , ' found'].

But as you can see there are many specific cases: CompiledMethod, bytes objects, word objects, immediate objects, variable-sized objects, weak objects and for Pharo 4 even others that you may need to handle in your code (Ephemerons, 2bytes and 4 bytes objects).

If you don't get the specific cases (you may not know programming language internals), then imagine how you would make your code work to initialize an Array, a ByteArray or a CompiledMethod from a dictionary. Not easy, huh ?

That's why I strongly recommend to use something like STON, because it is very easy to use, handle already all the specific cases, well documented (Sven always does fancy documentation) and it will be maintained in Pharo 4 for recent changes (because Sven likes to use the bleeding edge version of Pharo).
        
Regards,

Clement


2014-05-22 19:37 GMT+02:00 sergio_101 <[hidden email]>:

is it possible to initialize a class with a dictionary? my first thought would be to create a method like:

intializeWithDictionary: aDictionary

then, loop through the elements and do something like:

instVarNamed: key put: value

but the book says:

Caveat: Although these methods are useful for building development tools, using them to develop conventional applications is a bad idea: these reflective methods break the encapsulation boundary of your objects and can there- fore make your code much harder to understand and maintain.-- 

should i avoid this?
sergio_101
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Re: Initializing a class with a Dictionary

sergio_101
great! looking at STON next! thanks!


On Thu, May 22, 2014 at 2:26 PM, Clément Bera <[hidden email]> wrote:
Hello,

I think you should look at the STON framework. STON looks like JSON for smalltalk objects. Basically it does the same as your idea but instead of a dictionary it loads fields of an objects from a STON file which looks like a JSON file (a STON is kind of an extended Dictionary exported as a string, but it has support for more that instance variables).

Now if you want to go your way, to me what you want to do looks fine. These methods can be used for development tools but also for frameworks and stuff like that. The thing to do it is to add this method in Object and add support so it can work on all objects in the system.

Object>>#intializeWithDictionary: aDictionary
    self class isVariable ifTrue: ["specific case ?"]
    self class isBytes ifTrue: ["specific case ?"]
    self class isCompiledMethod ifTrue: ["specific case ?"]
    self class isSmallInteger ifTrue: ["specific case"]
    aDictionary keysAndValuesDo: [ :key :value |
        self instVarNamed: key put: value ifAbsent: [ self error: 'no ', key , ' found'].

But as you can see there are many specific cases: CompiledMethod, bytes objects, word objects, immediate objects, variable-sized objects, weak objects and for Pharo 4 even others that you may need to handle in your code (Ephemerons, 2bytes and 4 bytes objects).

If you don't get the specific cases (you may not know programming language internals), then imagine how you would make your code work to initialize an Array, a ByteArray or a CompiledMethod from a dictionary. Not easy, huh ?

That's why I strongly recommend to use something like STON, because it is very easy to use, handle already all the specific cases, well documented (Sven always does fancy documentation) and it will be maintained in Pharo 4 for recent changes (because Sven likes to use the bleeding edge version of Pharo).
        
Regards,

Clement


2014-05-22 19:37 GMT+02:00 sergio_101 <[hidden email]>:


is it possible to initialize a class with a dictionary? my first thought would be to create a method like:

intializeWithDictionary: aDictionary

then, loop through the elements and do something like:

instVarNamed: key put: value

but the book says:

Caveat: Although these methods are useful for building development tools, using them to develop conventional applications is a bad idea: these reflective methods break the encapsulation boundary of your objects and can there- fore make your code much harder to understand and maintain.-- 

should i avoid this?






--
Clément Béra
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Re: Initializing a class with a Dictionary

Clément Béra



2014-05-22 21:11 GMT+02:00 sergio_101 <[hidden email]>:
great! looking at STON next! thanks!

You can find it in the configuration browser 

On Thu, May 22, 2014 at 2:26 PM, Clément Bera <[hidden email]> wrote:
Hello,

I think you should look at the STON framework. STON looks like JSON for smalltalk objects. Basically it does the same as your idea but instead of a dictionary it loads fields of an objects from a STON file which looks like a JSON file (a STON is kind of an extended Dictionary exported as a string, but it has support for more that instance variables).

Now if you want to go your way, to me what you want to do looks fine. These methods can be used for development tools but also for frameworks and stuff like that. The thing to do it is to add this method in Object and add support so it can work on all objects in the system.

Object>>#intializeWithDictionary: aDictionary
    self class isVariable ifTrue: ["specific case ?"]
    self class isBytes ifTrue: ["specific case ?"]
    self class isCompiledMethod ifTrue: ["specific case ?"]
    self class isSmallInteger ifTrue: ["specific case"]
    aDictionary keysAndValuesDo: [ :key :value |
        self instVarNamed: key put: value ifAbsent: [ self error: 'no ', key , ' found'].

But as you can see there are many specific cases: CompiledMethod, bytes objects, word objects, immediate objects, variable-sized objects, weak objects and for Pharo 4 even others that you may need to handle in your code (Ephemerons, 2bytes and 4 bytes objects).

If you don't get the specific cases (you may not know programming language internals), then imagine how you would make your code work to initialize an Array, a ByteArray or a CompiledMethod from a dictionary. Not easy, huh ?

That's why I strongly recommend to use something like STON, because it is very easy to use, handle already all the specific cases, well documented (Sven always does fancy documentation) and it will be maintained in Pharo 4 for recent changes (because Sven likes to use the bleeding edge version of Pharo).
        
Regards,

Clement


2014-05-22 19:37 GMT+02:00 sergio_101 <[hidden email]>:


is it possible to initialize a class with a dictionary? my first thought would be to create a method like:

intializeWithDictionary: aDictionary

then, loop through the elements and do something like:

instVarNamed: key put: value

but the book says:

Caveat: Although these methods are useful for building development tools, using them to develop conventional applications is a bad idea: these reflective methods break the encapsulation boundary of your objects and can there- fore make your code much harder to understand and maintain.-- 

should i avoid this?






--

stepharo
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Re: Initializing a class with a Dictionary

stepharo
In reply to this post by sergio_101
Hi sergio

what do you want to do?


Object subclass: #MyClass
     instanceVarNames: 'dict'

MyClass>>initialize
     [
     super initialize.
     dict := Dictionary new.
     ]

MyClass>>atKey: aKey put: aVal
     [
     dict at: aKey put: aVal
     ]

MyClass>>atKey: aKey
     [
     ^ dict at: aKey
     ]

let you manage the key/val that you want?
Let me know if this answers your question.
Stef


On 22/5/14 19:37, sergio_101 wrote:

>
> is it possible to initialize a class with a dictionary? my first
> thought would be to create a method like:
>
> intializeWithDictionary: aDictionary
>
> then, loop through the elements and do something like:
>
> instVarNamed: key put: value
>
> but the book says:
>
> Caveat: Although these methods are useful for building development
> tools, using them to develop conventional applications is a bad idea:
> these reflective methods break the encapsulation boundary of your
> objects and can there- fore make your code much harder to understand
> and maintain.--
>
> should i avoid this?
>
>
> ----
> peace,
> sergio
> photographer, journalist, visionary
> #BitMessage BM-2D8VWUJSS41RFKh1ec83preVabHrnniExa
>
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> http://www.facebook.com/sergio101
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