Making method with default encoding

[Tommi Prami 130]

as far as I know I cant do something like (at least compiler did not like that)
 

procedure Save(const AData:TStringList; const AEncoding: TEncoding = TEncoding.UTF8);
begin
  AData.SaveToFile(FileName, AEncoding);
end;

Is there any standard way to pass encoding default (For certain case). Quick look did not give any results (RTL code adn Google) 

Edited April 29, 2020 by Tommi Prami

[Lars Fosdal 1792]

TEncoding.Default ?

[David Heffernan 2345]

39 minutes ago, Lars Fosdal said:

TEncoding.Default ?

Default values need to be true constants. This is not. 

 

You are confusing default encoding with default parameter value. 

Edited April 29, 2020 by David Heffernan

[Uwe Raabe 2057]

I guess you have to use overload methods.

 

function Format(const Format: string; const Args: array of const): string; overload;
function Format(const Format: string; const Args: array of const;  const AFormatSettings: TFormatSettings): string; overload;

 

[David Heffernan 2345]

38 minutes ago, Tommi Prami said:

Is there any standard way to pass encoding default

You can't declare an encoding instance to be a default parameter value because it is not a constant, never mind a true constant. Hence the compiler error. 

 

So you have to resort to overloaded methods. Declare one method that accepts an encoding parameter. And another that does not. From that second overload call the first passing your chosen default encoding. 

[Attila Kovacs 629]

for TEncoding you can set it nil as default and use your favorite one (as default) if the param is nil

[Lars Fosdal 1792]

A helper type / class could be an alternative.

TEncodingType = (encDefault, encUTF7, encUTF8, encUnicode, encBigEndianUnicode, encMBCS, encExpandThisTypeAsNeeded);

TEncodingHelper = record helper for TEncodingType
  function Encoding: TEncoding; overload; // which calls the method below with Self
  function Encoding(const aEncodingType: TEncodingType): TEncoding; overload; // which look up the relevant TEncoding constants.
end;

 

[Tommi Prami 130]

I clarify little.

what mean by Default, not the Delphi default but MY DEFAULT what it ever would be. in current context.

I also was thinking of using enumerated type or so, but it is not that official, Delphi defined way. Seems that this has not been thought at all while implementing this. There are ways around this, but seems no way to define some (random) defaulöt method parameter.

 

-Tee-

[Lars Fosdal 1792]

TEncodingType = (encDefault, encUTF7, encUTF8, encUnicode, encBigEndianUnicode, encMBCS, encExpandThisTypeAsNeeded);

TEncodingHelper = record helper for TEncodingType
private class var
  FMyDefault: TEncodingType;
public
  function Encoding: TEncoding; overload; // which calls the method below with Self
  function Encoding(const aEncodingType: TEncodingType): TEncoding; overload; // which look up the relevant TEncoding constants.
  class property FMyDefault: TEncodingType read FMyDefault write FMyDefault;
end;

 

[David Heffernan 2345]

30 minutes ago, Tommi Prami said:

I clarify little.

what mean by Default, not the Delphi default but MY DEFAULT what it ever would be. in current context.

I also was thinking of using enumerated type or so, but it is not that official, Delphi defined way. Seems that this has not been thought at all while implementing this. There are ways around this, but seems no way to define some (random) defaulöt method parameter.

 

-Tee-

This provides no clarification to me. Now I think I have no idea what you are asking. 

[Remy Lebeau 1393]

Being a class type, you really can't specify a specific TEncoding value as a default parameter value.  So you have to either:

 

Use an overload (that is what Delphi's RTL does):

procedure Save(const AData: TStringList); overload;
procedure Save(const AData: TStringList; const AEncoding: TEncoding); overload;

...

procedure Save(const AData: TStringList);
begin
  Save(AData, TEncoding.UTF8);
end;

procedure Save(const AData: TStringList; const AEncoding: TEncoding);
begin
  AData.SaveToFile(FileName, AEncoding);
end;

Or else use nil for the default value:

procedure Save(const AData: TStringList; AEncoding: TEncoding = nil);

...

procedure Save(const AData: TStringList; AEncoding: TEncoding);
begin
  if AEncoding = nil then AEncoding := TEncoding.UTF8;
  AData.SaveToFile(FileName, AEncoding);
end;

 

Edited April 29, 2020 by Remy Lebeau

[Fr0sT.Brutal 900]

I'd prefer using nil as a sign of taking some previously configured encoding. Or, if you dare, you could use code page numbers.