# Inverse OOP **URL:** \ **Category:** Ruby\ **Created:** [April 24, 2008, 11:39am UTC](https://www.ruby-forum.com/t/inverse-oop/135708 "2008-04-24T11:39:58Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![martin\_gnu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@martin\_gnu](https://www.ruby-forum.com/u/martin_gnu)\ **Post date:** [April 24, 2008, 11:39am UTC](https://www.ruby-forum.com/t/inverse-oop/135708/1 "2008-04-24T11:39:58Z")
Hi: 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. All map proyections have the same methods (geodetic\_to\_projected and projected\_to\_geodetic) Regards. ---
**Author:** ![martin\_gnu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@martin\_gnu](https://www.ruby-forum.com/u/martin_gnu)\ **Post date:** [April 24, 2008, 12:16pm UTC](https://www.ruby-forum.com/t/inverse-oop/135708/2 "2008-04-24T12:16:57Z")
On 24 Apr 2008, at 10:40, Martin V. wrote: > projected\_to\_geodetic) > Then define either a projection class from which they all inherit, or > a projection module which they all include. Ellie ## Eleanor McHugh Games With Brains [http://slides.games-with-brains.net](http://slides.games-with-brains.net) raise ArgumentError unless @reality.responds\_to? :reason ---
**Author:** ![martin\_gnu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@martin\_gnu](https://www.ruby-forum.com/u/martin_gnu)\ **Post date:** [April 24, 2008, 11:25pm UTC](https://www.ruby-forum.com/t/inverse-oop/135708/3 "2008-04-24T23:25:42Z")
On 24.04.2008 12:15, Eleanor McHugh wrote: > On 24 Apr 2008, at 10:40, Martin V. 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)? > > All map proyections have the same methods (geodetic\_to\_projected and > > projected\_to\_geodetic) > > Then define either a projection class from which they all inherit, or > a projection module which they all include. Nice reading from you again, Ellie. 🙂 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? Cheers robert ---
**Author:** ![martin\_gnu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@martin\_gnu](https://www.ruby-forum.com/u/martin_gnu)\ **Post date:** [April 25, 2008, 1:55am UTC](https://www.ruby-forum.com/t/inverse-oop/135708/4 "2008-04-25T01:55:03Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Apr 24, 2008, at 11:40 AM, Martin V. wrote: > Hi: > > 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.?? Actually, thats quite a common problem of thought, because inheritance is often considered as _the_ problem solver in OOP. But that is not the case. I for my part seldomly inherit. The core feature of OOP is composition. So even without modules, you could just implement a class that has a certain set of features and hands everything else to a class that has a concrete implementation for that task (delegation, btw. 😉 ). Depending on the language, this can get large because of the vast amount of boilerplate code you have to write for the delegating methods, but in Ruby, this is a simple task. Regards, Florian G. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (Darwin) iEYEARECAAYFAkgRHZ8ACgkQJA/zY0IIRZbPZgCgp/Vx54NYWH6PppPXRENXic3s OwEAn2SFwl0BnIJsu+fvc4+RUBlUGbn/ =tD69 -----END PGP SIGNATURE----- ---
**Author:** ![martin\_gnu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@martin\_gnu](https://www.ruby-forum.com/u/martin_gnu)\ **Post date:** [April 24, 2008, 11:45pm UTC](https://www.ruby-forum.com/t/inverse-oop/135708/5 "2008-04-24T23:45:05Z")
Robert K. wrote: > On 24.04.2008 12:15, Eleanor McHugh wrote: > > > On 24 Apr 2008, at 10:40, Martin V. 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/](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?? ---
**Author:** ![martin\_gnu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@martin\_gnu](https://www.ruby-forum.com/u/martin_gnu)\ **Post date:** [April 25, 2008, 3:26am UTC](https://www.ruby-forum.com/t/inverse-oop/135708/6 "2008-04-25T03:26:18Z")
On 24 Apr 2008, at 22:45, Martin V. wrote: > Okay. then this is a multiple inheritance problem?? I hate telling other people how to code, but yes it looks very much like a multiple inheritance problem. Ellie ## Eleanor McHugh Games With Brains [http://slides.games-with-brains.net](http://slides.games-with-brains.net) raise ArgumentError unless @reality.responds\_to? :reason ---
**Author:** ![martin\_gnu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@martin\_gnu](https://www.ruby-forum.com/u/martin_gnu)\ **Post date:** [April 25, 2008, 3:23am UTC](https://www.ruby-forum.com/t/inverse-oop/135708/7 "2008-04-25T03:23:57Z")
On 24 Apr 2008, at 22:25, Robert K. wrote: > 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)? > > > > All map proyections have the same methods (geodetic\_to\_projected and > > > projected\_to\_geodetic) > > > Then define either a projection class from which they all inherit, > > > or a projection module which they all include. And if these functions are included from a module their names should be to\_projected and to\_geodetic as it doesn’t matter to other classes what they’re being translated from. > Nice reading from you again, Ellie. 🙂 Damn, I’ve gone and blown my anonymity again 😉 > 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? That was my reaction. I did a lot of similar work many years ago when I was a VB hacker and abstracted projections using interfaces, which are marginally similar to Ruby’s modules, but it’s possible Martin has some more complicated use case in mind. Ellie ## Eleanor McHugh Games With Brains [http://slides.games-with-brains.net](http://slides.games-with-brains.net) raise ArgumentError unless @reality.responds\_to? :reason ---
**Author:** ![martin\_gnu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@martin\_gnu](https://www.ruby-forum.com/u/martin_gnu)\ **Post date:** [April 29, 2008, 12:16am UTC](https://www.ruby-forum.com/t/inverse-oop/135708/8 "2008-04-29T00:16:12Z")
Thanks all hehe ---
**Author:** ![martin\_gnu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/edb3f5/32.png) [@martin\_gnu](https://www.ruby-forum.com/u/martin_gnu)\ **Post date:** [April 26, 2008, 2:46pm UTC](https://www.ruby-forum.com/t/inverse-oop/135708/9 "2008-04-26T14:46:03Z")
On 25.04.2008 03:25, Eleanor McHugh wrote: > On 24 Apr 2008, at 22:45, Martin V. wrote: > > > Okay. then this is a multiple inheritance problem?? > > I hate telling other people how to code, but yes it looks very much > like a multiple inheritance problem. In fact, wasn’t that exactly what Martin mentioned in his first posting: a class that inherits from multiple parents? So basically MI is just the name for what he described in the first place. Kind regards robert