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program tw38122;
{$mode objfpc}
{$modeswitch advancedrecords}
{$modeswitch typehelpers}
uses
Math;
type float = double;
pfloat = ^float;
type TFloatHelper = type helper for float
procedure sub (const a: float);
end;
type TMatrix = record
sx,sy: sizeint;
procedure Init (x,y: sizeint; content: array of float);
function GetAdr (x,y: sizeint): pfloat;
procedure print;
private
data: array of float;
end;
procedure TFloatHelper.sub (const a: float);
begin
self := self-a;
end;
function TMatrix.GetAdr (x,y: sizeint): pfloat;
begin
result := @data[x*sy+y];
end;
procedure TMatrix.Init (x,y: sizeint; content: array of float);
var i: sizeint;
begin
sx :=x;
sy :=y;
Data := nil;
SetLength (data, sx*sy);
for i := 0 to sx*sy-1 do data[i] := content[i];
end;
procedure TMatrix.print;
var x,y: sizeint;
begin
for y := 0 to sy-1 do begin
writeln;
for x := 0 to sx-1 do begin
write (GetAdr(x,y)^:2:2,' ');
end;
end;
writeln;
end;
var A: TMatrix;
px: pfloat;
begin
A.Init (2,2,[1,2,3,4]);
A.print;
if not SameValue(A.data[3],4,1e-1) then
Halt(1);
A.GetAdr(1,1)^ := 0; //I can set an element like this...
A.Print;
if not SameValue(A.data[3],0,1e-1) then
Halt(2);
px := A.GetAdr(1,1);
px^.sub(100); //and this works as well.
A.Print;
if not SameValue(A.data[3],-100,1e-1) then
Halt(3);
A.GetAdr(1,1)^.sub(1000); //but that does not change the Matrix !?!
A.print;
if not SameValue(A.data[3],-1100,1e-1) then
Halt(4);
end.
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