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Dealing with multiple cases of a string while keeping code short and OOP friendly

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kilon.alios

Dealing with multiple cases of a string while keeping code short and OOP friendly

So I am parsing strings that represent python types and other custom objects. An example would be

'<Vector (1.0 , 0.2 , 0.8) >' or '<Color (0.3 , 0.9 , 0.4 )>'

etc

But I dont want to use too many ifTrue , ifFalse and end up with a long method.

So I was thinking creating a OrderedCollection that would be 2D , first dimension is the regex that fits the type the second is the pharo object that corresponds to this type . Then I will have a common method for each of those pharo object to deal with the parsing.

But I was wondering how to use a class that I dont know its name until runtime. For example lets say i get a string

aPythonString := '< Bone [ "side bone" , IK = True , ( 1.0 , 0.1 , 0.2) ]>'

I would want in this case to send the message the EphBoneType parse : aPythonString. The problem is that I dont know the contents of the string until I receive it. So I want the name of the class to be composed according the string received .

Is this possible ? Is this a smart way ? How would you do it ?

Sean P. DeNigris

Re: Dealing with multiple cases of a string while keeping code short and OOP friendly

Administrator

kilon.alios wrote

Is this possible ? Is this a smart way ? How would you do it ?

IIUC I would parse just enough to separate the class name from the data, and then let each subclass parse the data. Something like:
PythonObject fromString: '< Bone [ "side bone" , IK = True , ( 1.0 , 0.1 , 0.2) ]>'.
where:
PythonObject>>#fromString: aString
| bracketContents pythonClassName data class |
bracketContents := aString allButFirst allButLast trimBoth.
pythonClassName := bracketContents copyUpTo: Character space.
data := bracketContents copyAfter: Character space.
class := self subclasses detect: [ :c | c pythonClassName = pythonClassName ].
^ class data: data.

Cheers,
Sean

kilon.alios

Re: Dealing with multiple cases of a string while keeping code short and OOP friendly

oh Sean this so beautiful and elegant, exactly what I was looking for. Thank you very much.

The rest of your code is what I was thinking doing with regex instead.

This was the part I was not aware of

class := self subclasses detect: [ :c | c pythonClassName = pythonClassName

On Mon, Mar 9, 2015 at 11:02 PM, Sean P. DeNigris <[hidden email]> wrote:

kilon.alios wrote
> Is this possible ? Is this a smart way ? How would you do it ?

IIUC I would parse just enough to separate the class name from the data, and
then let each subclass parse the data. Something like:
PythonObject fromString: '< Bone [ "side bone" , IK = True , ( 1.0 , 0.1
, 0.2) ]>'.
where:
PythonObject>>#fromString: aString
| bracketContents pythonClassName data class |
bracketContents := aString allButFirst allButLast trimBoth.
pythonClassName := bracketContents copyUpTo: Character space.
data := bracketContents copyAfter: Character space.
class := self subclasses detect: [ :c | c pythonClassName = pythonClassName
].
^ class data: data.

-----
Cheers,
Sean
--
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Sean P. DeNigris

Re: Dealing with multiple cases of a string while keeping code short and OOP friendly

Administrator

kilon.alios wrote

oh Sean this so beautiful and elegant
class := self subclasses detect: [ :c | c pythonClassName =
pythonClassName

Yes I like/use this pattern a lot! I think I learned it from "A Mentoring Course on Smalltalk"

Cheers,
Sean

kilon.alios

Re: Dealing with multiple cases of a string while keeping code short and OOP friendly

I have seen a similar pattern in Kent Beck book Smalltalk Patterns , but I was not sure this was a good way to go in this case .

So I thought that would not hurt to ask for a second opinion from a more experienced Pharo coder.

On Tue, Mar 10, 2015 at 12:03 AM, Sean P. DeNigris <[hidden email]> wrote:

kilon.alios wrote
> oh Sean this so beautiful and elegant
> class := self subclasses detect: [ :c | c pythonClassName =
> pythonClassName

Yes I like/use this pattern a lot! I think I learned it from "A Mentoring
Course on Smalltalk"

-----
Cheers,
Sean
--
View this message in context: http://forum.world.st/Dealing-with-multiple-cases-of-a-string-while-keeping-code-short-and-OOP-friendly-tp4810731p4810790.html

Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com.