[fpc-pascal] Help creating generic class: division problem
Martin
fpc at mfriebe.de
Mon Apr 5 16:13:16 CEST 2010
If it is only between int and double, maybe this will help
have on overload function
class function TMedian.Div(Value, Divider: Integer): Integer; // Result
:= Value div Divider
class function TMedian.Div(Value, Divider: Double): Double; // Result
:= Value / Divider
then the compiler chooses dependent on T.
On 05/04/2010 15:04, leledumbo wrote:
> consider the following generic class declaration:
>
> {$mode objfpc}{$H+}
>
> type
> generic TMedian<T> = class
> class function Find(x: array of T): T;
> end;
>
> class function TMedian.Find(x: array of T): T;
> var
> i, j, Middle: Integer;
> Temporary: T;
> begin
> // Use truncated selection sort to find median
> Middle := (High(x) + 1) div 2;
> for i := 0 to Middle do
> for j := 1 to High(x) - i do
> if x[j]> x[j - 1] then begin
> Temporary := x[j];
> x[j] := x[j - 1];
> x[j - 1] := Temporary;
> end;
> if Odd(High(x)) then
> // When High(x) is Odd, there are an even number of elements in array.
> // Define median as average of two middle values.
> Result := (x[Middle] + x[Middle - 1]) / 2 //<-- This line
> else
> // When High(x) is Even, there are an odd number of elements in array.
> // Median is the middle value.
> Result := x[Middle];
> end {Find};
>
> How can I make it work such that:
>
> type
> TMedianInteger = specialize TMedian<Integer>;
> TMedianDouble = specialize TMedian<Double>;
>
> is valid?
>
> See the line marked with<-- above, due to semantic of /, I can't use
> integer because / returns floating point value, Extended to be precise. If I
> change it to div, it won't work (correctly) for floating point values,
> because the precision is lost. Typecasting to T won't work either because
> Extended can't be converted to LongInt (larger to smaller type problem).
>
>
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