Re: [fpc-pascal] how to pass a procedure address and execute it?
On 1/23/2014 2:18 PM, waldo kitty wrote: following up on this, how do i pass parameters to doThis and doThat?? do i have to use an intermediate pre_doThis and pre_doThat which handles the calls from centralControl and then calls doThis and doThat with the necessary parameters? type TProc = Procedure; procedure doThis(aRecord : somerec;); begin addRecord(aRecord); end; procedure doThat(outFile : textfile; aRecord : somerec;); begin writefile(outFile,aRecord); end; procedure pre_doThis; begin doThis(theRecord); end; procedure pre_doThat; begin doThat(oFile,theRecord); end; procedure centralControl(var aValue : word; theRecord : somerec; whichProc : TProc); begin case aValue of 0 : begin whichProc; end; 1 : begin if theRecord^.aValue = something then whichProc; end; end; procedure inputThis; begin centralControl(foo,thisRecord,@pre_doThis); end; procedure outputThat; begin centralControl(foo,thisRecord,@pre_doThat); end; -- NOTE: No off-list assistance is given without prior approval. Please keep mailing list traffic on the list unless private contact is specifically requested and granted. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] how to pass a procedure address and execute it?
On 24 Jan 2014, at 21:20, waldo kitty wrote: On 1/23/2014 2:18 PM, waldo kitty wrote: following up on this, how do i pass parameters to doThis and doThat?? do i have to use an intermediate pre_doThis and pre_doThat which handles the calls from centralControl and then calls doThis and doThat with the necessary parameters? Simply change the type: Type TProc = Procedure(aRecord: somerec); Then you can call whichProc (in centralControl) with your argument of choice. -- Ewald ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] how to pass a procedure address and execute it?
On 1/24/2014 3:18 PM, Ewald wrote: On 24 Jan 2014, at 21:20, waldo kitty wrote: On 1/23/2014 2:18 PM, waldo kitty wrote: following up on this, how do i pass parameters to doThis and doThat?? do i have to use an intermediate pre_doThis and pre_doThat which handles the calls from centralControl and then calls doThis and doThat with the necessary parameters? Simply change the type: Type TProc = Procedure(aRecord: somerec); Then you can call whichProc (in centralControl) with your argument of choice. ahhh! that helps to explain what the compiler error was that i was seeing... so i may need two different types if each procedure called from centralControl has different parameters? won't that cause a conflict if the parameters are not the same or are in different ordering or even if some procedure doesn't have parameters at all? -- NOTE: No off-list assistance is given without prior approval. Please keep mailing list traffic on the list unless private contact is specifically requested and granted. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] how to pass a procedure address and execute it?
On 24 Jan 2014, at 22:20, waldo kitty wrote: On 1/24/2014 3:18 PM, Ewald wrote: On 24 Jan 2014, at 21:20, waldo kitty wrote: On 1/23/2014 2:18 PM, waldo kitty wrote: following up on this, how do i pass parameters to doThis and doThat?? do i have to use an intermediate pre_doThis and pre_doThat which handles the calls from centralControl and then calls doThis and doThat with the necessary parameters? Simply change the type: Type TProc = Procedure(aRecord: somerec); Then you can call whichProc (in centralControl) with your argument of choice. ahhh! that helps to explain what the compiler error was that i was seeing... so i may need two different types if each procedure called from centralControl has different parameters? Basically yes (if you mean different parameter types/ different parameter order -- the name in the procedure/function type is merely descriptive AFAIK). But if you have many procedures, I'd go for a class: TCentralControl = Class Protected Procedure Callback1; virtual; abstract; Procedure Callback2(value: TSomeRec); virtual; abstract; Function Callback3: Boolean; virtual abstract; ... and so on ... Public Procedure CentralControl(.); End; Then simply inherit from this class a few times for the different scenario's you want to cover. won't that cause a conflict if the parameters are not the same or are in different ordering or even if some procedure doesn't have parameters at all? Yes, you would need a lot of parameters if you need a lot of callbacks. if this is the case go for the OOP approach; it is perfectly suited for this kind of thing. -- Ewald ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] how to pass a procedure address and execute it?
ahhh! that helps to explain what the compiler error was that i was seeing... so i may need two different types if each procedure called from centralControl has different parameters? won't that cause a conflict if the parameters are not the same or are in different ordering or even if some procedure doesn't have parameters at all? Yes, of course. If you want to implement something like callback, the parameters have to be consistent. You can't pass arbitrary procedure as it would violate the type safe property. One idea would be to have all possible procedures implement the same parameter list, but only use some of them in the implementation. This could slow down the processing a bit but if speed is not really an issue I don't think you should care. -- View this message in context: http://free-pascal-general.1045716.n5.nabble.com/how-to-pass-a-procedure-address-and-execute-it-tp5718103p5718117.html Sent from the Free Pascal - General mailing list archive at Nabble.com. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] how to pass a procedure address and execute it?
On 23 Jan 2014, at 20:18, waldo kitty wrote: i'm trying to use one routine (centralControl) to process data from two different routines (inputThis and outputThat)... the one routine (centralControl) needs to call one of two other routines (doThis or doThat)... how? :( First define a type to make your like easier: Type TProcType: Procedure; Next, adjust contralContol's prototype: procedure centralControl(var aValue : word; theRecord : somerec; whichProc: TProcType); And you're done:-) -- Ewald ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] how to pass a procedure address and execute it?
In our previous episode, waldo kitty said: i'm trying to use one routine (centralControl) to process data from two different routines (inputThis and outputThat)... the one routine (centralControl) needs to call one of two other routines whichproc is typeless and thus roughly equal to a pointer to a byte (though semantically different, and add another pointer indirection for the VAR). So the compiler doesn't know what to do with it. how? :( Define a procedure type that matches both procedures, in your example Type TProc = procedure ; // which is predefined in system afaik. and change whichproc to that type. The VAR is not necessary in this case. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] how to pass a procedure address and execute it?
On 1/23/2014 1:27 PM, Marco van de Voort wrote: Define a procedure type that matches both procedures, in your example Type TProc = procedure ; // which is predefined in system afaik. and change whichproc to that type. The VAR is not necessary in this case. Alternately, switch to an OOP model, whose entire model (inheritance) addresses this sort of thing. -- Jim Leonard (trix...@oldskool.org) Check out some trippy MindCandy: http://www.mindcandydvd.com/ A child borne of the home computer wars: http://trixter.oldskool.org/ You're all insane and trying to steal my magic bag! ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] how to pass a procedure address and execute it?
On 1/23/2014 2:22 PM, Ewald wrote: On 23 Jan 2014, at 20:18, waldo kitty wrote: i'm trying to use one routine (centralControl) to process data from two different routines (inputThis and outputThat)... the one routine (centralControl) needs to call one of two other routines (doThis or doThat)... how? :( First define a type to make your like easier: Type TProcType: Procedure; Next, adjust contralContol's prototype: procedure centralControl(var aValue : word; theRecord : somerec; whichProc: TProcType); And you're done:-) damn! i was so close so many times! i did try using pointer as the type with and without 'var' for whichProc... this will be a huge savings in time and code size! thanks! -- NOTE: No off-list assistance is given without prior approval. Please keep mailing list traffic on the list unless private contact is specifically requested and granted. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] how to pass a procedure address and execute it?
On 1/23/2014 2:27 PM, Marco van de Voort wrote: In our previous episode, waldo kitty said: i'm trying to use one routine (centralControl) to process data from two different routines (inputThis and outputThat)... the one routine (centralControl) needs to call one of two other routines whichproc is typeless and thus roughly equal to a pointer to a byte (though semantically different, and add another pointer indirection for the VAR). So the compiler doesn't know what to do with it. how? :( Define a procedure type that matches both procedures, in your example Type TProc = procedure ; // which is predefined in system afaik. and change whichproc to that type. The VAR is not necessary in this case. excellent! as noted in a previous post, i was so close several times ;) -- NOTE: No off-list assistance is given without prior approval. Please keep mailing list traffic on the list unless private contact is specifically requested and granted. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] how to pass a procedure address and execute it?
On 1/23/2014 2:32 PM, Jim Leonard wrote: On 1/23/2014 1:27 PM, Marco van de Voort wrote: Define a procedure type that matches both procedures, in your example Type TProc = procedure ; // which is predefined in system afaik. and change whichproc to that type. The VAR is not necessary in this case. Alternately, switch to an OOP model, whose entire model (inheritance) addresses this sort of thing. interesting... i do use customapplication for the main program so i can take advantage of getoption and friends... i wonder... hummm... -- NOTE: No off-list assistance is given without prior approval. Please keep mailing list traffic on the list unless private contact is specifically requested and granted. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
