Why ObjectBinaryToText does not support vaCurrency in ReadPropList.

[dmitryb]

Hi All

Why Classes.inc - procedure ObjectBinaryToText does not support vaCurrency in ReadPropList.

In the ProcessValue procedure
    procedure ProcessValue(ValueType: TValueType; Indent: String);

...

          end;
        {vaSingle: begin OutLn('!!Single!!'); exit end;
        vaCurrency: begin OutLn('!!Currency!!'); exit end;
        vaDate: begin OutLn('!!Date!!'); exit end;}
        vaUTF8String: begin
...

they just comment out code that read vaCurrency values.


I have components with list of Vairants as property value.
When value in list have vaCurrency value, writing data to text file crashed.

[howardpc]

Floating point values cannot be published.
If you want real value fields in a class their visibility cannot be higher than public.
(later) Well, I was completely wrong about that!

[dmitryb]

Hello

I tested component with Currency and Variant

Code: Pascal  [Select][+][-]

1.   TComponentWithCurr = class(TComponent)
2.   private
3.     FCurrProp: Currency;
4.     FVarProp: Variant;
5.   protected
6.     procedure DefineProperties(Filer: TFiler); override;
7.     procedure DoReadData(Reader: TReader); virtual;
8.     procedure DoWriteData(Writer: TWriter); virtual;
9.   public
10.  
11.   published
12.     property CurrProp: Currency read FCurrProp write FCurrProp;
13.     property VarProp: Variant read FVarProp write FVarProp;
14.   end;  

It works without problem.

[dmitryb]

Our values are not in published section.
They are written in DefineProperties.

[Thaddy]

Our values are not in published section.
They are written in DefineProperties.

In that case make sure the properties are defined in {$M+} mode. That doesn't  happen automatically, so use {$push}{$M+} ... definition ...{$pop} otherwise no rtti is generated and you have the behavior as you described.

[marcov]

Our values are not in published section.
They are written in DefineProperties.

In that case make sure the properties are defined in {$M+} mode. That doesn't  happen automatically, so use {$push}{$M+} ... definition ...{$pop} otherwise no rtti is generated and you have the behavior as you described.

Afaik he inherits from tcomponent which inherits from TPersistent which is declared with {$M+}, so his class inherits that status.

[Thaddy]

I just mentioned it, just in case.

[ASerge]

Currency like other floating types can be published:

Code: Pascal  [Select][+][-]

1. type
2.   TSomeClass = class(TComponent)
3.   strict private
4.     FCurrProp: Currency;
5.   published
6.     property CurrProp: Currency read FCurrProp write FCurrProp;
7.   end;
8.  
9. procedure TForm1.Button1Click(Sender: TObject);
10. var
11.   One, Two: TSomeClass;
12.   MemStream: TMemoryStream;
13.   StrStream: TStringStream;
14. begin
15.   One := TSomeClass.Create(Self);
16.   One.CurrProp := 1.23456;
17.   MemStream := TMemoryStream.Create;
18.   try
19.     MemStream.WriteComponent(One);
20.     StrStream := TStringStream.Create('');
21.     try
22.       MemStream.Position := 0;
23.       ObjectBinaryToText(MemStream, StrStream);
24.       Memo1.Text := StrStream.DataString;  // 1
25.       MemStream.Position := 0;
26.       StrStream.Position := 0;
27.       ObjectTextToBinary(StrStream, MemStream);
28.     finally
29.       StrStream.Free;
30.     end;
31.     MemStream.Position := 0;
32.     RegisterClass(TSomeClass);
33.     Two := MemStream.ReadComponent(nil) as TSomeClass;
34.     try
35.       Memo1.Append(CurrToStr(Two.CurrProp)); // 2
36.     finally
37.       Two.Free;
38.     end;
39.   finally
40.     MemStream.Free;
41.   end;
42. end;

All floating types are written as Extended, so there is no separate code for Single, Date, etc.

[jamie]

isn't a Currency a 64 bit binary type? Two 32 bits ?

[Thaddy]

Yes. (but) it is a scaled integer type internally https://freepascal.org/docs-html/ref/refsu5.html

[jamie]

I guess my hint was that if the READER / WRITER is going to translate it to a float then it's possible to lose accuracy, maybe.

[Thaddy]

I guess my hint was that if the READER / WRITER is going to translate it to a float then it's possible to lose accuracy, maybe.

No, because of the inherit limitation of currency. You have to check how the compiler handles it if you want the details.
Basically it is the storage format.