From: Martin Vales <martin@...>
Date: 2008-04-25T06:45:08+09:00
Subject: Re: inverse OOP

Robert Klemme wrote:
> On 24.04.2008 12:15, Eleanor McHugh wrote:
>> On 24 Apr 2008, at 10:40, Martin Vales wrote:
> 
>>> I have always had a doubt about OOP.
>>> Usually we have a parent and several child, but what happen if we need
>>> the inverse system. for example DBI/DBD APIs.??
>>>
>>> I need build map proyections and i want and intermediate API for all
>>> proyections clases.
> 
> What exactly do you mean by "intermediate"?  Do you mean that all
> projections should have the same interface?  For that you do not need
> inheritance at all - at least in Ruby.  Or do you rather mean that they
> share behavior (implementation)?

Same interface:

For example


This is the intermediate API
#type="projection=lambert, varphi_0=45, k=1"
type="projection=UTM, zone=30, false_east=40000"
prj=Projection.new(type)

[x,y]=prj.geodetic_to_projected(lambda,phi)
[lambda,phi]=prj.projected_to_geodetic(x,y)


This is an especific API for UTM:

parameters=UtmParameters.new
parameters.zone=30
parameters.false_east=30
prj=UtmProjection.new(parameters)

[x,y]=prj.utm_geodetic_to_projected(lambda,phi)
[lambda,phi]=prj.utm_projected_to_geodetic(x,y)

This is an especific API for lambert:

parameters=LambertParameters.new
parameters.varphi_0=30
parameters.k=1
prj=LambertProjection.new(parameters)

[x,y]=prj.lambert_geodetic_to_projected(lambda,phi)
[lambda,phi]=prj.lambert_projected_to_geodetic(x,y)



I have used the proj.4 C library and they used pointers to functions in 
C, in a offuscated code.

http://proj.maptools.org/

proj.4 use a text file like this:
"projection=lambert, varphi_0=45, k=1"

Every projection is an module (ANSI C file) and a only modulo know what 
module call using the text file. There are 170 different projections.

  +proj=cea +lon_0=Central Meridian
            +lat_ts=Standard Parallel
            +x_0=False Easting
            +y_0=False Northing


+proj=lcc   +lat_1=Latitude of natural origin
             +lon_0=Longitude of natural origin
             +k_0=Scale factor at natural origin
             +x_0=False Origin Easting
             +y_0=False Origin Northing

  +proj=tmerc +lat_0=Latitude of natural origin
              +lon_0=Longitude of natural origin
              +k=Scale factor at natural origin
              +x_0=False Easting
              +y_0=False Northing


...

> 
> I was going to also suggest the module approach.  But I do wonder why
> Martin chose to call it "inverse OOP".  It seems the more appropriate
> term would be "multiple inheritance" or am I missing something?

Okay. then this is a multiple inheritance problem??


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