Am 25.04.2018 um 08:34 schrieb Ryan Joseph: > >> On Apr 25, 2018, at 12:59 PM, Sven Barth via fpc-pascal >> <fpc-pascal@lists.freepascal.org> wrote: >> >> No. This would more often than not lead to accidents were users pass such an >> instance to some outer code (it doesn't even need to the routine with the >> stack object, but some third party routine that for some reason stores the >> pointer and is called from that routine) and then will trigger an exception >> in the best case or hard to debug errors in the worst case. > I assume if programmers care enough about performance they’re planning out > memory usage by stack vs heap they know not to do that. The pointer is only > alive for the duration of the scope. I thought this was a good idea because > it explicitly lets you opt in when know you really need it and it’s discreet. > > If c++ programmers know not to do that why don’t Pascal programmers? There’s > endless ways to screw yourself with memory in general (especially in c++) but > we still find a way.
If you know what you are doing, you have exactly the "object" type for that. You can allocate them on the stack or heap and you can inherit from them, when you need virtual methods the initialization is a bit strange (and if you need performance virtual methods are wrong anyway). The benefit is better performance when needed. The downside is that they are more unsafe to use than "class" type and you should now what you do. If I need a cheap (performance wise) "procedure of object" for example, that can't escape from the scope I use them instead of a class: type TDataArray = array of Integer; TFilterData = function(element: Integer): Boolean of object; function FilterData(const data: array of Integer; filter: TFilterData): TDataArray; var i, lr, el: Integer; begin Result:= nil; lr:= 0; for el in data do begin if filter(el) then begin SetLength(result, lr + 1); result[lr]:= el; inc(lr); end; end; end; type TTestClosure = object val: Integer; function less(element: Integer): Boolean; end; function TTestClosure.less(element: Integer): Boolean; begin Result:= element < val; end; procedure Test; var stack: TTestClosure; data: TDataArray; begin stack.val:= 10; data:= FilterData([2,4,8,10,12], stack.less); assert(Length(data) = 3); end; _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
