* Package hierarchy. Extensibility. @ 2009-03-12 0:02 Jarno Neniu 2009-03-12 7:26 ` Niklas Holsti 0 siblings, 1 reply; 5+ messages in thread From: Jarno Neniu @ 2009-03-12 0:02 UTC (permalink / raw) Hello. I'm not able to decide about which design is the best (extensibility, maintainability and recompilation friendliness are important), so I'm demanding for any humble and not so humble opinions. As an example of hierarchy consider representation of geometrical points. One of representations is preferable and considered to be the main representation (Cartesian 2D and 3D points), but there is unspecified amount of other representations, which could be added to the system later (points in polar, spherical, cylindrical coordinate systems). Conversion between representations should be somehow available and it is desirable for representations to be generic. Which is the best way to design the hierarchy? Should it be something like this: package Points is -- Preferable representation. Cartesian point. type Point is ... end Points; package Points.Spherical is type Spherical_Point is ... end Points.Spherical; package Points.Cylindrical is type Cylindrical_Point is ... end Points.Cylindrical; Or should it be dummy package «Points» to which other representations are connected: package Points is end Points; package Points.Cartesian is type Cartesian_Point is ... end Points.Cartesian; package Points.Spherical is type Spherical_Point is ... end Points.Spherical; Something else? ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Package hierarchy. Extensibility. 2009-03-12 0:02 Package hierarchy. Extensibility Jarno Neniu @ 2009-03-12 7:26 ` Niklas Holsti 2009-03-13 1:31 ` Jarno 0 siblings, 1 reply; 5+ messages in thread From: Niklas Holsti @ 2009-03-12 7:26 UTC (permalink / raw) Jarno Neniu wrote: > Hello. I'm not able to decide about which design is the best > (extensibility, maintainability and recompilation friendliness are > important), so I'm demanding for any humble and not so humble > opinions. As an example of hierarchy consider representation of > geometrical points. One of representations is preferable and > considered to be the main representation (Cartesian 2D and 3D points), > but there is unspecified amount of other representations, which could > be added to the system later (points in polar, spherical, cylindrical > coordinate systems). Conversion between representations should be > somehow available and it is desirable for representations to be > generic. Which is the best way to design the hierarchy? Should it be > something like this: > > package Points is > -- Preferable representation. Cartesian point. > type Point is ... > end Points; > > package Points.Spherical is > type Spherical_Point is ... > end Points.Spherical; > > package Points.Cylindrical is > type Cylindrical_Point is ... > end Points.Cylindrical; > > Or should it be dummy package �Points� to which other representations > are connected: > > package Points is > end Points; > > package Points.Cartesian is > type Cartesian_Point is ... > end Points.Cartesian; > > package Points.Spherical is > type Spherical_Point is ... > end Points.Spherical; > > Something else? An interface type that defines the common view of "Points" of whatever representation? That would allow non-hierarchical and independent implementations of the representations as long as every representation implements this interface. -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Package hierarchy. Extensibility. 2009-03-12 7:26 ` Niklas Holsti @ 2009-03-13 1:31 ` Jarno 2009-03-13 10:58 ` Niklas Holsti 0 siblings, 1 reply; 5+ messages in thread From: Jarno @ 2009-03-13 1:31 UTC (permalink / raw) Niklas Holsti: > An interface type that defines the common view of "Points" of > whatever representation? That would allow non-hierarchical and > independent implementations of the representations as long as every > representation implements this interface. Can you please post a simple example? Does interface means extendable type («interface» or «tagged»)? I think run-time dispatching would be too much heavy. Seems that I need to organize a bunch of generic interconvertible types and still be able to add other representations later with minimal cost. ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Package hierarchy. Extensibility. 2009-03-13 1:31 ` Jarno @ 2009-03-13 10:58 ` Niklas Holsti 2009-03-13 11:03 ` Niklas Holsti 0 siblings, 1 reply; 5+ messages in thread From: Niklas Holsti @ 2009-03-13 10:58 UTC (permalink / raw) Jarno wrote: > Niklas Holsti: > >> An interface type that defines the common view of "Points" of >> whatever representation? That would allow non-hierarchical and >> independent implementations of the representations as long as >> every representation implements this interface. > > Can you please post a simple example? Does interface means > extendable type (�interface� or �tagged�)? Yes, I meant types that extend (implement) an interface type. I had in fact missed that your original posting did not make these "Point" types tagged, that is, you did not ask about a *type* hierarchy but only about a *package* hierarchy. This being the case, I don't see enough information in your original posting to answer your question. If these types have nothing else in common but their use to represent 2D or 3D points, and the existence of conversions between them, there is little basis for evaluating your alternatives. The only reason for using child packages would be to organize your package names hierarchically, which is of course nice but introduces unnecessary compilation dependencies, especially if you declare the "preferable representation" in the common parent package. So that much can be answered: to minimize compilation dependencies, parent packages should contain only stuff that is common (in some sense) to all children. You also said: > .. it is desirable for representations to be generic. By "generic", do you mean that you will have generic units that take a formal type parameter to specify which "Point" representation they use? Such as: generic type Point_Type is private; <formal operations on Point_Type> procedure Rotate_Figure ... If so, you must ensure that the various kinds of "Point" all implement compatible operations, to be associated with the <formal operations> in the generic instances. If you use a tagged type hierarchy or an interface type, operations like Rotate_Figure can be class-wide, rather than generic, or can avoid the declaration of <formal operations> by using instead the primitive operations of the formal type parameter. > Seems that I need to organize a bunch of generic > interconvertible types and still be able to add other > representations later with minimal cost. Do you need conversion from any "point" type to any other "point" type? That would be a quadratic number of conversions, which is to be avoided, of course. If all "point" types implement a common interface, you could write a single "constructor" function for each "point" type, say PT, that creates an object of type PT from any parameter that implements this interface. This single function can then be used to convert any other "point" object to an object of type PT. There may be a small decrease in floating-point numerical accuracy in this approach, because it is like first converting the source type to a "preferable" type (the interface), and then from there to the target type, with round-offs in both conversions. > I think run-time dispatching would be too much heavy. Using tagged types or interfaces has two penalties: extra space in each object to store the tag, and extra execution time *if* run-time dispatching is used. But I sense that you want to have different "point" representations because you want to use the most suitable representation for each algorithm. If you write your algorithms as type-specific rather class-wide, the compiler should bind all operations statically, even if the types are tagged. The need to assign and copy tags implies a (small) time penalty even if operations are statically bound. If this is important to you, or if the space overhead of tags is important, I would recommend a two-layer approach: define the various "Point" types as untagged, and then define a "wrapping" tagged type hierarchy (or interface-implementing types) that has some such untagged "Point" type as a component. You can then write your type-specific algorithms using the untagged types, and "wrap" them into objects of the tagged type(s) when you want to be class-wide. For example: -- The untagged representations: type Cartesian_Point is record .. end record; type Spherical_Point is record .. end record; -- The tagged representations: type Tagged_Point is abstract tagged null record; type Tagged_Cartesian_Point is new Tagged_Point with record Point : Cartesian_Point; end record; type Spherical_Cartesian_Point is new Tagged_Point with record Point : Spherical_Point; end record; -- The algorithms: procedure Cartesian_Algo (P : Cartesian_Point) is ... procedure Spherical_Algo (P : Spherical_Point) is ... procedure Class_Wide_Algo (P : Tagged_Point'Class) is ... HTH, -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Package hierarchy. Extensibility. 2009-03-13 10:58 ` Niklas Holsti @ 2009-03-13 11:03 ` Niklas Holsti 0 siblings, 0 replies; 5+ messages in thread From: Niklas Holsti @ 2009-03-13 11:03 UTC (permalink / raw) Whoops: Niklas Holsti wrote: > type Spherical_Cartesian_Point is new Tagged_Point > with record Point : Spherical_Point; end record; I meant: > type Tagged_Spherical_Point is new Tagged_Point > with record Point : Spherical_Point; end record; Sorry... -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2009-03-13 11:03 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2009-03-12 0:02 Package hierarchy. Extensibility Jarno Neniu 2009-03-12 7:26 ` Niklas Holsti 2009-03-13 1:31 ` Jarno 2009-03-13 10:58 ` Niklas Holsti 2009-03-13 11:03 ` Niklas Holsti
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