| Groups | Blog | Home |
dotnet general : Casting base class to inherited one
[quoted text, click to view]
On Jul 30, 8:47 pm, jan.lou...@gmail.com wrote: > Hi, > We're building a mapping application and inside we're using open > source dll called MapServer. This dll uses object model that has quite > a few classes. In our app we however need to little bit modify come of > the classes so they match our purpose better - mostly add a few > methods etc. > Example: Open source lib has classes Map and Layer defined. The > relationship between them is one to many. > We created our own versions (inherited) of Map called OurMap and our > version of Layer called OurLayer. The only difference between them is > that they have some extra methods (because we need them to do little > bit extra). > Is there any way how can I convert the base class (either Map or > Layer) to our inherited one (OurMap or OurLayer)? > I know that implicit or explicit conversion operators don't work > between inherited and base class Who told you that? It's certainly not true. C# allows you to write your own conversion operator, either implicit or explicit, that copies the members from your base class object into a new, derived class object, and return the derived object. The only hitch, of course, is that you end up with a copy, but there's no way around that.
[quoted text, click to view]
On Jul 30, 9:00 pm, jan.lou...@gmail.com wrote: > On Jul 31, 11:52 am, Bruce Wood <brucew...@canada.com> wrote: > > > > > > > On Jul 30, 8:47 pm, jan.lou...@gmail.com wrote: > > > > Hi, > > > We're building a mapping application and inside we're using open > > > source dll called MapServer. This dll uses object model that has quite > > > a few classes. In our app we however need to little bit modify come of > > > the classes so they match our purpose better - mostly add a few > > > methods etc. > > > Example: Open source lib has classes Map and Layer defined. The > > > relationship between them is one to many. > > > We created our own versions (inherited) of Map called OurMap and our > > > version of Layer called OurLayer. The only difference between them is > > > that they have some extra methods (because we need them to do little > > > bit extra). > > > Is there any way how can I convert the base class (either Map or > > > Layer) to our inherited one (OurMap or OurLayer)? > > > I know that implicit or explicit conversion operators don't work > > > between inherited and base class > > > Who told you that? It's certainly not true. C# allows you to write > > your own conversion operator, either implicit or explicit, that copies > > the members from your base class object into a new, derived class > > object, and return the derived object. > > > The only hitch, of course, is that you end up with a copy, but there's > > no way around that. > > When I try that the compiler complains: > C:\MapServer\IntraMaps60\SpatialEngineWS\Layers > \IntraMapsLayer.cs(208): 'DMS.IntraMaps.IntraMapsLayer.implicit > operator DMS.IntraMaps.IntraMapsLayer(layerObj)': user-defined > conversion to/from base class > I googled it and I found some articles that you cannot implicitly > convert from base class to it's child. > Am I doing something wrong? Could you post the code you wrote? Both your definition of the implicit conversion operator and your use of it?
[quoted text, click to view]
On Jul 30, 9:43 pm, Bruce Wood <brucew...@canada.com> wrote: > On Jul 30, 9:00 pm, jan.lou...@gmail.com wrote: > > > > > > > On Jul 31, 11:52 am, Bruce Wood <brucew...@canada.com> wrote: > > > > On Jul 30, 8:47 pm, jan.lou...@gmail.com wrote: > > > > > Hi, > > > > We're building a mapping application and inside we're using open > > > > source dll called MapServer. This dll uses object model that has quite > > > > a few classes. In our app we however need to little bit modify come of > > > > the classes so they match our purpose better - mostly add a few > > > > methods etc. > > > > Example: Open source lib has classes Map and Layer defined. The > > > > relationship between them is one to many. > > > > We created our own versions (inherited) of Map called OurMap and our > > > > version of Layer called OurLayer. The only difference between them is > > > > that they have some extra methods (because we need them to do little > > > > bit extra). > > > > Is there any way how can I convert the base class (either Map or > > > > Layer) to our inherited one (OurMap or OurLayer)? > > > > I know that implicit or explicit conversion operators don't work > > > > between inherited and base class > > > > Who told you that? It's certainly not true. C# allows you to write > > > your own conversion operator, either implicit or explicit, that copies > > > the members from your base class object into a new, derived class > > > object, and return the derived object. > > > > The only hitch, of course, is that you end up with a copy, but there's > > > no way around that. > > > When I try that the compiler complains: > > C:\MapServer\IntraMaps60\SpatialEngineWS\Layers > > \IntraMapsLayer.cs(208): 'DMS.IntraMaps.IntraMapsLayer.implicit > > operator DMS.IntraMaps.IntraMapsLayer(layerObj)': user-defined > > conversion to/from base class > > I googled it and I found some articles that you cannot implicitly > > convert from base class to it's child. > > Am I doing something wrong? > > Could you post the code you wrote? Both your definition of the > implicit conversion operator and your use of it? Forget it. I just read the C# spec on line, here: http://msdn2.microsoft.com/en-us/library/aa664464(VS.71).aspx It says quite clearly that I'm wrong: you cannot provide implicit or explicit conversions either up or down the class hierarchy. Which means that the only option left open to you is a copy constructor: your derived class must have a constructor that accepts a member of your base class, like this: public class Derived : Base { public Derived(Base baseObject) { ... } } or, you could make it a static method in your derived class: public static Derived DerivedFromBase(Base baseObject) { ... } Bummer about the conversions, though. I guess it causes some sort of problem within the CLR....
[quoted text, click to view]
On Jul 31, 12:43 pm, Bruce Wood <brucew...@canada.com> wrote: > On Jul 30, 9:00 pm, jan.lou...@gmail.com wrote: > > > > > On Jul 31, 11:52 am, Bruce Wood <brucew...@canada.com> wrote: > > > > On Jul 30, 8:47 pm, jan.lou...@gmail.com wrote: > > > > > Hi, > > > > We're building a mapping application and inside we're using open > > > > source dll called MapServer. This dll uses object model that has quite > > > > a few classes. In our app we however need to little bit modify come of > > > > the classes so they match our purpose better - mostly add a few > > > > methods etc. > > > > Example: Open source lib has classes Map and Layer defined. The > > > > relationship between them is one to many. > > > > We created our own versions (inherited) of Map called OurMap and our > > > > version of Layer called OurLayer. The only difference between them is > > > > that they have some extra methods (because we need them to do little > > > > bit extra). > > > > Is there any way how can I convert the base class (either Map or > > > > Layer) to our inherited one (OurMap or OurLayer)? > > > > I know that implicit or explicit conversion operators don't work > > > > between inherited and base class > > > > Who told you that? It's certainly not true. C# allows you to write > > > your own conversion operator, either implicit or explicit, that copies > > > the members from your base class object into a new, derived class > > > object, and return the derived object. > > > > The only hitch, of course, is that you end up with a copy, but there's > > > no way around that. > > > When I try that the compiler complains: > > C:\MapServer\IntraMaps60\SpatialEngineWS\Layers > > \IntraMapsLayer.cs(208): 'DMS.IntraMaps.IntraMapsLayer.implicit > > operator DMS.IntraMaps.IntraMapsLayer(layerObj)': user-defined > > conversion to/from base class > > I googled it and I found some articles that you cannot implicitly > > convert from base class to it's child. > > Am I doing something wrong? > > Could you post the code you wrote? Both your definition of the > implicit conversion operator and your use of it? This is my inherited class: public class IntraMapsLayer : layerObj { public IntraMapsLayer(superMapObj map) : base (map) { this.currentSuperMapObj = map; } public static implicit operator IntraMapsLayer(layerObj layer) { IntraMapsLayer newLayer = new IntraMapsLayer(this.map); newLayer.bandsitem = layer.bandsitem; newLayer.classitem = layer.classitem; newLayer.connection = layer.connection; newLayer.connectiontype = layer.connectiontype; newLayer.data = layer.data; newLayer.debug = layer.debug; newLayer.dump = layer.dump; //newLayer.extent = layer.extent; newLayer.filteritem = layer.filteritem; newLayer.footer = layer.footer; newLayer.group = layer.group; newLayer.header = layer.header; //newLayer.index = layer.index; newLayer.labelangleitem = layer.labelangleitem; newLayer.labelcache = layer.labelcache; newLayer.labelitem = layer.labelitem; newLayer.labelmaxscale = layer.labelmaxscale; newLayer.labelminscale = layer.labelminscale; newLayer.labelrequires = layer.labelrequires; newLayer.labelsizeitem = layer.labelsizeitem; //newLayer.map = layer.map; newLayer.maxfeatures = layer.maxfeatures; newLayer.maxscale = layer.maxscale; //newLayer.metadata = layer.metadata; newLayer.minscale = layer.minscale; newLayer.name = layer.name; //newLayer.numclasses = layer.numclasses; //newLayer.numitems = layer.numitems; //newLayer.numjoins = layer.numjoins; //newLayer.numprocessing = layer.numprocessing; newLayer.offsite = layer.offsite; newLayer.plugin_library = layer.plugin_library; newLayer.plugin_library_original = layer.plugin_library_original; newLayer.postlabelcache = layer.postlabelcache; newLayer.requires = layer.requires; newLayer.sizeunits = layer.sizeunits; newLayer.status = layer.status; newLayer.styleitem = layer.styleitem; newLayer.symbolscale = layer.symbolscale; newLayer.template = layer.template; newLayer.tileindex = layer.tileindex; newLayer.tileitem = layer.tileitem; newLayer.tolerance = layer.tolerance; newLayer.toleranceunits = layer.toleranceunits; newLayer.transform = layer.transform; newLayer.transparency = layer.transparency; newLayer.type = layer.type; newLayer.units = layer.units; return newLayer; } this implicit operator does not even compile. I haven't mentioned it yet but we're bound to .NET 1.1 unfortunatelly
[quoted text, click to view]
On Jul 31, 12:51 pm, Bruce Wood <brucew...@canada.com> wrote: > On Jul 30, 9:43 pm, Bruce Wood <brucew...@canada.com> wrote: > > > > > On Jul 30, 9:00 pm, jan.lou...@gmail.com wrote: > > > > On Jul 31, 11:52 am, Bruce Wood <brucew...@canada.com> wrote: > > > > > On Jul 30, 8:47 pm, jan.lou...@gmail.com wrote: > > > > > > Hi, > > > > > We're building a mapping application and inside we're using open > > > > > source dll called MapServer. This dll uses object model that has quite > > > > > a few classes. In our app we however need to little bit modify come of > > > > > the classes so they match our purpose better - mostly add a few > > > > > methods etc. > > > > > Example: Open source lib has classes Map and Layer defined. The > > > > > relationship between them is one to many. > > > > > We created our own versions (inherited) of Map called OurMap and our > > > > > version of Layer called OurLayer. The only difference between them is > > > > > that they have some extra methods (because we need them to do little > > > > > bit extra). > > > > > Is there any way how can I convert the base class (either Map or > > > > > Layer) to our inherited one (OurMap or OurLayer)? > > > > > I know that implicit or explicit conversion operators don't work > > > > > between inherited and base class > > > > > Who told you that? It's certainly not true. C# allows you to write > > > > your own conversion operator, either implicit or explicit, that copies > > > > the members from your base class object into a new, derived class > > > > object, and return the derived object. > > > > > The only hitch, of course, is that you end up with a copy, but there's > > > > no way around that. > > > > When I try that the compiler complains: > > > C:\MapServer\IntraMaps60\SpatialEngineWS\Layers > > > \IntraMapsLayer.cs(208): 'DMS.IntraMaps.IntraMapsLayer.implicit > > > operator DMS.IntraMaps.IntraMapsLayer(layerObj)': user-defined > > > conversion to/from base class > > > I googled it and I found some articles that you cannot implicitly > > > convert from base class to it's child. > > > Am I doing something wrong? > > > Could you post the code you wrote? Both your definition of the > > implicit conversion operator and your use of it? > > Forget it. I just read the C# spec on line, here: > > http://msdn2.microsoft.com/en-us/library/aa664464(VS.71).aspx > > It says quite clearly that I'm wrong: you cannot provide implicit or > explicit conversions either up or down the class hierarchy. > > Which means that the only option left open to you is a copy > constructor: your derived class must have a constructor that accepts a > member of your base class, like this: > > public class Derived : Base > { > public Derived(Base baseObject) > { > ... > } > > } > > or, you could make it a static method in your derived class: > > public static Derived DerivedFromBase(Base baseObject) { ... } > > Bummer about the conversions, though. I guess it causes some sort of > problem within the CLR.... I didn't get what was the copy constructor supposed to do - can u explain it to me?
[quoted text, click to view]
> Who told you that? It's certainly not true. C# allows you to write > your own conversion operator, either implicit or explicit, that copies > the members from your base class object into a new, derived class > object, and return the derived object. So does VB .NET 2005.
Hi,
We're building a mapping application and inside we're using open source dll called MapServer. This dll uses object model that has quite a few classes. In our app we however need to little bit modify come of the classes so they match our purpose better - mostly add a few methods etc. Example: Open source lib has classes Map and Layer defined. The relationship between them is one to many. We created our own versions (inherited) of Map called OurMap and our version of Layer called OurLayer. The only difference between them is that they have some extra methods (because we need them to do little bit extra). Is there any way how can I convert the base class (either Map or Layer) to our inherited one (OurMap or OurLayer)? I know that implicit or explicit conversion operators don't work between inherited and base class but I was just wondering if there is another way how to do this or if there's something wrong with our object design? Thanks for any help
[quoted text, click to view]
On Jul 31, 11:52 am, Bruce Wood <brucew...@canada.com> wrote: > On Jul 30, 8:47 pm, jan.lou...@gmail.com wrote: > > > > > Hi, > > We're building a mapping application and inside we're using open > > source dll called MapServer. This dll uses object model that has quite > > a few classes. In our app we however need to little bit modify come of > > the classes so they match our purpose better - mostly add a few > > methods etc. > > Example: Open source lib has classes Map and Layer defined. The > > relationship between them is one to many. > > We created our own versions (inherited) of Map called OurMap and our > > version of Layer called OurLayer. The only difference between them is > > that they have some extra methods (because we need them to do little > > bit extra). > > Is there any way how can I convert the base class (either Map or > > Layer) to our inherited one (OurMap or OurLayer)? > > I know that implicit or explicit conversion operators don't work > > between inherited and base class > > Who told you that? It's certainly not true. C# allows you to write > your own conversion operator, either implicit or explicit, that copies > the members from your base class object into a new, derived class > object, and return the derived object. > > The only hitch, of course, is that you end up with a copy, but there's > no way around that. When I try that the compiler complains: C:\MapServer\IntraMaps60\SpatialEngineWS\Layers \IntraMapsLayer.cs(208): 'DMS.IntraMaps.IntraMapsLayer.implicit operator DMS.IntraMaps.IntraMapsLayer(layerObj)': user-defined conversion to/from base class I googled it and I found some articles that you cannot implicitly convert from base class to it's child. Am I doing something wrong?
Don't see what you're looking for? Try a search.
|
June 2003
July 2003
August 2003
September 2003
October 2003
November 2003
December 2003
January 2004
February 2004
March 2004
April 2004
May 2004
June 2004
July 2004
August 2004
September 2004
October 2004
November 2004
December 2004
January 2005
February 2005
March 2005
April 2005
May 2005
June 2005
July 2005
August 2005
September 2005
October 2005
November 2005
December 2005
January 2006
February 2006
March 2006
April 2006
May 2006
June 2006
July 2006
August 2006
September 2006
October 2006
November 2006
December 2006
January 2007
February 2007
March 2007
April 2007
May 2007
June 2007
July 2007
August 2007
September 2007
October 2007
November 2007
December 2007
January 2008
February 2008
March 2008
April 2008
| home · blog · groups | Questions? Comments? Contact the dn |