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Multiextending
Posted: Sat May 31, 2008 7:14 am
by Hroudtwolf
Hi,
I've a little wish again.
It would be very cool, if you could make it possible, that we can use more than one
extends with structures.
In example:
Code: Select all
Structure cLayer Extends cBase Extends tLayer
EndStructure
The constructing of datasets, based on propertyfragments would be very easy.
Best regards
Wolf
Posted: Sat May 31, 2008 11:35 am
by Mistrel
+1
Posted: Sat May 31, 2008 11:46 am
by eesau
What happens when both cBase and tLayer have a structure field with the same name?
Posted: Sat May 31, 2008 12:51 pm
by Mistrel
eesau wrote:What happens when both cBase and tLayer have a structure field with the same name?
It would probably result in a compiler error. :roll:
Posted: Sat May 31, 2008 6:35 pm
by Trond
That will destroy the whole concept of Extends, which is that the fields are placed
first in the structure, so that the structure can be passed to functions expecting a pointer to the old structure.
This is how it works:
Code: Select all
Structure SShape
Color.l
EndStructure
Structure SRectangle Extends SShape
Width.l
Height.l
EndStructure
Procedure SShape_GetColor(*Shape.SShape)
ProcedureReturn *Shape\Color
EndProcedure
My.SRectangle\Color = $deadbeef
Debug Hex(SShape_GetColor(@My))
Multi-extending is impossible, because the fields of SSoccerField and SShape can't
both be placed first in SRectangle. That will make the code above mysteriously fail on this rectangle.
Code: Select all
Structure SSoccerField
NumberOfPlayers.l
EndStructure
Structure SShape
Color.l
EndStructure
Structure SRectangle Extends SSoccerField Extends SShape
Width.l
Height.l
EndStructure