Strange result at with result do
lazarus / 21-General

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Hansvb · 2024-06-30 17:45

Hi,

See TestFun_1. I understand that it is not useful to call all
variables "S", but why is the incoming s not assigned to the result s?
TestFun_2 works well. The only difference is that 1 var is now renamed
to t.

I tested in lazarus 3.4, 3.0 and 2.4. (on Windows). All 3 give the
same result.

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 unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics, Dialogs, StdCtrls; type  PDummy = ^TDummy;  TDummy
= record    s: String;  end;    { TForm1 }   TForm1 = class(TForm)   
Button1: TButton;    Button2: TButton;    Edit1: TEdit;    procedure
Button1Click(Sender: TObject);    procedure Button2Click(Sender:
TObject);  private    function TestFun_1(s: String): TDummy;   
function TestFun_2(t: String): TDummy;  public   end; var  Form1:
TForm1; implementation {$R *.lfm} { TForm1 } procedure
TForm1.Button1Click(Sender: TObject);var  lRec : TDummy;begin  lRec :=
TestFun_1('some text');  Edit1.Text:= lRec.s;end; procedure
TForm1.Button2Click(Sender: TObject);var  lRec : TDummy;begin  lRec :=
TestFun_2('some text');  Edit1.Text:= lRec.s;end;  function
TForm1.TestFun_1(s: String): TDummy;begin  With Result do begin    s:=
s;   // Returns nothing even the incoming "s: String" holds a value. 
end;end; function TForm1.TestFun_2(t: String): TDummy;begin  With
Result do begin    s:= t;  // works fine.  end;end; end.

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jamie · 2024-06-30 18:00

that's because both "S" are the same one.

The result S is empty and you just setting itself to itself.

the WITH is localizing the scope to the single S

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WooBean · 2024-06-30 18:06

Quote from: Hansvb on June 30, 2024, 07:45:25 pmHi,

See TestFun_1. I understand that it is not useful to call all
variables "S", but why is the incoming s not assigned to the result s?
TestFun_2 works well. The only difference is that 1 var is now renamed
to t.

I tested in lazarus 3.4, 3.0 and 2.4. (on Windows). All 3 give the
same result.

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
TForm1.TestFun_1(s: String): TDummy;begin  With Result do begin    s:=
s;   // Returns nothing even the incoming "s: String" holds a value. 
end;end;  
Nothing strange - where is "s" declaration searched?
First - inside Result record, as "s" field is found then is used.

In Pascal code
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   s:=s; 
 does nothing.

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
TForm1.TestFun_1(s: String): TDummy;begin  Result.s:=s; //it will do
what you wantend;

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cdbc · 2024-06-30 18:14

Hi
IMHO this: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  
PDirectoriesRec = ^TDirectoriesRec;  TDirectoriesRec = record   
dirNewDirnames, { TODO }    dirProjectName, { dunno, could be useful.
==> Now it is :) }    dirRoot,    dirSuccesMsg: string;   
dirPrjNameInDir: Boolean;    dirSucces: boolean;  end; is a much
better naming-convention i.e.: prefixing the fields in the record with
the versals of the record type-name... in the above case 'dir'.
That way if you can't remember the fields' names then you can, at
least figure it out and avoid name-clashes...
Regards Benny

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Thaddy · 2024-06-30 18:18

Close, but not completely correct: what happens is that the result
member variable s from TDummy as different scope. so you get with
Tdummy do ({TDummy.}s} := {Tdummy.}s
But the compiler warned you implicitly for that: warning result
variable seems not initialized and hint parameter s is not used.
Then again, ignoring warnings - and hints - , naming both s and using
with all in the same line of code isn't very sane.

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WooBean · 2024-06-30 18:29

Quote from: Thaddy on June 30, 2024, 08:18:37 pmClose, but not
completely correct: what happens is that the result variable s from
TDummy as different scope than the higher scoped parameter s.
But the compiler warned you implicitly for that: warning result
variable seems not initialized.
Then again, ignoring warnings, naming both s and using with all in the
same line of code isn't very sane.

To make an exercise more interesting I'd suggest a change  in type
TForm1:

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 TForm1 =
class(TForm)    Button1: TButton;    Button2: TButton;    Edit1:
TEdit;    procedure Button1Click(Sender: TObject);    procedure
Button2Click(Sender: TObject);  private    function TestFun_1(s:
String): TDummy;    function TestFun_2(t: String): TDummy;  public   
s:string;//then try to distinguish parameter of  function TestFun_1(s:
String): TDummy;  from class field.    end;

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Thaddy · 2024-06-30 18:35

To me it is an interesting excercise if you pay attention to warnings
and hints:
 Hint: (5024) Parameter "s" not used
 Warning: (5059) Function result variable does not seem to be
initialized

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Hansvb · 2024-06-30 19:26

The s parameter was for convenience in the example. But I did not look
at the hint or warnings. I'm going to check it out.

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Martin_fr · 2024-06-30 19:34

It seems you expected something like JS:

Code: Javascript  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i var x =
x;where the 2nd x is from the scope before the var.

But "with" isn't declaring "result". So any variable in the block (or
statement) that is covered by the "with" is treated equally.

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 with result
do s := s;translates to
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 result.s :=
result.s;

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Thaddy · 2024-06-30 19:37

If you click on the hint the IDE shows you that the parameter is not
used.
If you click on the warning it jumps to s:=s which is result.s :=
result.s and not initialized.
The combination of both tells you the block scope is with and the
compiler has no other information to solve that.