Geek Answers Handbook

Implicit conversion for overloaded write in Delphi as parameter in const array

We got rid of the short string as part of the conversion from Delphi 7. I wanted to make it as painless as possible, so we decided that we could change ShortString to some record that acted exactly the same. Here's how it is announced (there is more to it, but this is the main structure that describes the problem):

TShortStringRec = record 
private
  FStuff: array [0..49] of Char;
public
  class operator Implicit(AStuff: TShortStringRec): String;
  class operator Implicit(S1: String): TShortStringRec;
end;

This works well for setting strings to a record. But then functions such as formatthat are taken as a parameter const array of const. Is there a way to cast implict to what we want to pass to a const array?

function FunkyFunc : string;
var
  ssr : TShortStringRec;
begin
  ssr := 'Wall'; 
  result := format('Hello %s', [ssr]);  //<---error here
end;

Gives a syntax error during compilation because ssr is not a type of parameter that can be used on one of these arrays.

+5
3

: . . , , , - , , , . call- . "", , .

+7

:

function AsAnsiString : AnsiString;
function AsShortString : ShortString;

, :

result := Format('hello %s',[ssr.AsAnsiString]);
+2

- Delphi 2007, , Format() , . ( ) , ; "" . "AsAnsiString": , 1) , 2), , , .. TShortStringRec. AsAnsiString, , SetAsAnsiString ( AsAnsiString )? . , , .

string [], . , , AnsiChars ShortString, , UnicodeString, char [], :

type
 _ShortString3 = string[3]:
  ShortString3 = record
  private
    FData: _ShortString3;
    function GetAnsiChar(Index: Integer): AnsiChar;
    procedure PutAnsiChar(Index: Integer; const Value: AnsiChar);
  public
    class operator Implicit(const A: string): ShortString3;
    class operator Implicit(const A: ShortString3): string;
    class operator Equal(const A: ShortString3; B: AnsiChar): Boolean;
    class operator NotEqual(const A: ShortString3; B: AnsiChar): Boolean;
    class operator Equal(const A: ShortString3; B: ShortString3): Boolean;
    class operator NotEqual(const A: ShortString3; B: ShortString3): Boolean;
    class operator Add(const A: ShortString3; B: ShortString3): string;
    class operator Add(const A: ShortString3; B: AnsiChar): string;
    class operator Add(const A: ShortString3; B: string): string;
    property AnsiChars[Index: Integer]: AnsiChar read GetAnsiChar write PutAnsiChar; default;
end;

FWIW :

{ShortString3}

function ShortString3.GetAnsiChar(Index: Integer): AnsiChar;
begin
  Result := FData[Index];
end;

procedure ShortString3.PutAnsiChar(Index: Integer; const Value: AnsiChar);
begin
  FData[Index] := Value;
end;

class operator ShortString3.Implicit(const A: string): ShortString3;
begin
  Result.FData := _ShortString3(A);
end;

class operator ShortString3.Implicit(const A: ShortString3): string;
begin
  Result := string(A.FData);
end;

class operator ShortString3.Equal(const A: ShortString3; B: AnsiChar): Boolean;
begin
  Result := A.FData = B;
end;

class operator ShortString3.NotEqual(const A: ShortString3; B: AnsiChar): Boolean;
begin
  Result := A.FData <> B;
end;

class operator ShortString3.Equal(const A: ShortString3; B: ShortString3): Boolean;
begin
  Result := A.FData = B.FData;
end;

class operator ShortString3.NotEqual(const A: ShortString3; B: ShortString3): Boolean;
begin
  Result := A.FData <> B.FData;
end;

class operator ShortString3.Add(const A: ShortString3; B: ShortString3): string;
begin
  Result := string(A.FData + B.FData);
end;

class operator ShortString3.Add(const A: ShortString3; B: AnsiChar): string;
begin
  Result := string(A.FData + B);
end;

class operator ShortString3.Add(const A: ShortString3; B: string): string;
begin
  Result := string(A.FData) + B;
end;

, , 1 ShortString . ( , ShortString StringTypes , .) , ShortString, .

+1

More articles:


All Articles