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Report From: Delphi-BCB/Compiler/Delphi/Language/Overloading/Method [ Add a report in this area ]

Report #: 45318

Status: Closed

Sometimes compiler produces "Ambiguous call" error on overloaded methods, yet it shouldn't

Project: Delphi

Build #: 10.0.2288.42451

Version: 10.0

Submitted By: Vadim Yakovlev

Report Type: Minor failure / Design problem

Date Reported: 5/1/2007 3:00:29 PM

Severity: Infrequently encountered problem

Last Updated: 3/20/2012 2:24:39 AM

Platform: All platforms

Internal Tracking #: 249971

Resolution: Fixed (Resolution Comments)

Resolved in Build: : 12.0.3170.16989

Duplicate of: None

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Description

Consider this code. When I try to compile it, I get an error "Ambiguous call to A1" on a line C3.A1(AnsiString('')). It shouldn't be so. In all four classes, set of overloaded versions of A1 method are the same, with identical signatures, but somewhy only a call to String version of TClass3 produces this error, in other cases, compiler correctly selectes which method to call. If you comment out that line, then code compiles without any problems. Also, the last block of code, where TClass3 type instance is assigned to TClass1 type variable demonstrates that overriding works correctly, only selection of an overloaded method fails.

program Project1;

uses
  Dialogs;

type
  TClass1 = class
    procedure A1(const S:String); overload; virtual;
    procedure A1(const S:WideString); overload; virtual;
  end;

  TClass2 = class (TClass1)
    procedure A1(const S:String); override;
  end;

  TClass3 = class (TClass1)
    procedure A1(const S:WideString); override;
  end;

  TClass4 = class (TClass1)
    procedure A1(const S:String); override;
    procedure A1(const S:WideString); override;
  end;

{ TClass1 }

procedure TClass1.A1(const S: String);
begin
  ShowMessage('Ansi, 1');
end;

procedure TClass1.A1(const S: WideString);
begin
  ShowMessage('Wide, 1');
end;

{ TClass2 }

procedure TClass2.A1(const S: String);
begin
  ShowMessage('Ansi, 2');
end;

{ TClass3 }

procedure TClass3.A1(const S: WideString);
begin
  ShowMessage('Wide, 3');
end;

{ TClass4 }

procedure TClass4.A1(const S: String);
begin
  ShowMessage('Ansi, 4');
end;

procedure TClass4.A1(const S: WideString);
begin
  ShowMessage('Wide, 4');
end;

var C1: TClass1; C2: TClass2; C3: TClass3; C4: TClass4;

begin
  C1 := TClass1.Create;
  try
    C1.A1(AnsiString(''));
    C1.A1(WideString(''));
  finally
    C1.Free;
  end;

  C2 := TClass2.Create;
  try
    C2.A1(AnsiString(''));
    C2.A1(WideString(''));
  finally
    C2.Free;
  end;

  C3 := TClass3.Create;
  try
    C3.A1(AnsiString(''));  //This line produces an error
    C3.A1(WideString(''));
  finally
    C3.Free;
  end;

  C4 := TClass4.Create;
  try
    C4.A1(AnsiString(''));
    C4.A1(WideString(''));
  finally
    C4.Free;
  end;

  C1 := TClass3.Create;
  try
    C1.A1(AnsiString(''));
    C1.A1(WideString(''));
  finally
    C1.Free;
  end;
end.

Steps to Reproduce:

1. Attempt to compile attached demo, you get an error.

2. Comment out or remove line "C3.A1(AnsiString(''));" and copile again - now there are no more problems.

Workarounds

None

Attachment

None

Comments

None

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Delphi-BCB

Compiler

Delphi

Language

Overloading

Global
Method

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QualityCentral Delphi-BCB Compiler Delphi Language Overloading Global Method

Developer Tools

Database Tools

QualityCentral

Delphi-BCB

Compiler

Delphi

Language

Overloading

Global
Method