Use of generics crashes
lazarus / 62-General

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MountainQ · 2021-11-01 12:49

Hi everyone;

the following code runs without issue (copy and past in a simple
program); however when I uncomment the first line in
"TFA2dHelper.Apply" (and delete the rest); I do not get the identical
result but rather a "SIGFPE" error. I am not sure what goes wrong; any
help is appreciated.
The redefinition of MinValue is necessary as the correct overloaded
function is not automatically chosen.

Best to all

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
minimal_crash; {$mode objfpc}{$H+}{$modeswitch typehelpers} uses 
Classes, SysUtils, math;  type  TFA = array of double;  TFA2d = array
of TFA;   TFAfct = function(const Data: array of double): double;  
generic T2dArrayFct<_list2d, _list1d, _el, _fct1d> = class  type   
TApplyFct = function(const l: _list1d): _el;  public    class function
Apply(const L: _list2d; fct: _fct1d): _list1d;  end;   TFctFA2d =
specialize T2dArrayFct<TFA2d, TFA, double, TFAfct>;   TFA2dHelper =
type Helper for TFA2d    function Apply(fct: TFAfct): TFA; 
end;  class function T2dArrayFct.Apply(const L: _list2d; fct: _fct1d):
_list1d;var  i: integer;  _fct: TApplyFct;begin  _fct :=
TApplyFct(fct);  Result := Default(_list1d);  SetLength(Result,
Length(l));  for i := low(l) to high(l) do    result[i] :=
_fct(l[i]);end; function TFA2dHelper.Apply(fct: TFAfct): TFA;var  i:
integer;begin  //Result := TFctFA2d.Apply(self, fct);  Result :=
Default(TFA);  SetLength(Result, Length(self));  for i := low(self) to
high(self) do    result[i] := fct(self[i]);end; function
MinDValue(const fa: array of double): double;begin  result :=
MinValue(fa);end;  var  fa0: TFA2d;  i, j: integer;  fa: TFA;  f:
double; begin  fa0 := Default(TFA2d);  SetLength(fa0, 3, 5);  for i :=
0 to Length(fa0)-1 do    for j := 0 to Length(fa0[i])-1 do      fa0[i,
j] := i+j+1;  fa := fa0.Apply(@MinDValue);  for f in fa do   
writeln(f);  writeln('all done.');  readln();end.

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bytebites · 2021-11-01 17:20

Problem is not generics, but open array.
Change function type as follows:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i TFAfct =
function(const Data: TFa): double;
and function declaration too:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
MinDValue(const fa: TFa): double;begin  result := MinValue(fa);end;

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MountainQ · 2021-11-01 19:21

Thanks a lot bytebites; it instantly works;

could you point to some documentation to clarify the difference.

The use of open array seemed "consistent"; the problem did not arise
if no generics were used.

thanks again