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// This code is provided bt Leandro Conde [leandor@gmail.com]
// to demonstrate a problem with function redirection in interfaces
// in the FPC compiler version 2.0.2
//
// In the real implementation is used to provide a set of data type
// conversion functions: From<Type> and To<Type>.
// In that scenario, the IBase contains functions specific por <Type>,
// and the Derived are the <From> and <To> parts.
{$mode delphi}
program FunctionRedirectionProblem;
{$APPTYPE CONSOLE}
var
cnt : longint;
type
// It really doesn't matters what this interface contains,
// is just represet some functionality set that is provided
// with two complementary sets of implementations.
IBase = interface
['{6CEA50E0-1844-405F-9B6F-2E9D50BE6EFC}']
function Base1(const Arg1: string; const Arg2: Double): Boolean;
function Base2(const Arg1: TDateTime; const Arg2: Single): Boolean;
function Base3(const Arg1: WideString; const Arg2: Integer): Boolean;
end;
// Derived 1 to provide an IBase with a specific funtionality when used from IDerived1
IDerived1 = interface (IBase)
['{3DC49E1B-9A52-499E-8BCD-E1BA160329C9}']
function Derived1Specific(Arg1: Integer): Integer;
end;
// Derived 2 to provide an IBase with a complementary funtionality when used from IDerived2
IDerived2 = interface (IBase)
['{E44DF3BC-75C8-4284-928B-DE3162347C21}']
function Derived2Specific(Arg1: Integer): Integer;
end;
// Just for runtime testing purposes
ITestCase = interface
['{C608134F-2F9A-44A4-8932-F169EF40E177}']
function Derived1: IDerived1;
function Derived2: IDerived2;
end;
type
// Implementing all the above stuff
TTestCase = class(TInterfacedObject, IDerived1, IDerived2, ITestCase )
protected
// methods from IBase in IDerived1 redirected to one function set:
function IDerived1.Base1 = Derived1_Base1;
function IDerived1.Base2 = Derived1_Base2;
function IDerived1.Base3 = Derived1_Base3;
// this is the function set for IBase in IDerived1
function Derived1_Base1(const Arg1: string; const Arg2: Double): Boolean;
function Derived1_Base2(const Arg1: TDateTime; const Arg2: Single): Boolean;
function Derived1_Base3(const Arg1: WideString; const Arg2: Integer): Boolean;
// specifics from IDerived1
function Derived1Specific(Arg1: Integer): Integer;
protected
// methods from IBase in IDerived2 redirected to the other function set:
function IDerived2.Base1 = Derived2_Base1;
function IDerived2.Base2 = Derived2_Base2;
function IDerived2.Base3 = Derived2_Base3;
// this is the function set for IBase in IDerived2
function Derived2_Base1(const Arg1: string; const Arg2: Double): Boolean;
function Derived2_Base2(const Arg1: TDateTime; const Arg2: Single): Boolean;
function Derived2_Base3(const Arg1: WideString; const Arg2: Integer): Boolean;
// specifics from IDerived2
function Derived2Specific(Arg1: Integer): Integer;
protected // this is not essential, just for testing in runtime ITestCase
function Derived1: IDerived1;
function Derived2: IDerived2;
end;
{ TTestCase }
function TTestCase.Derived1_Base1(const Arg1: string; const Arg2: Double): Boolean;
begin
Result := True;
writeln('1:',arg1,arg2);
inc(cnt);
end;
function TTestCase.Derived1_Base2(const Arg1: TDateTime; const Arg2: Single): Boolean;
begin
Result := True;
end;
function TTestCase.Derived1_Base3(const Arg1: WideString; const Arg2: Integer): Boolean;
begin
Result := True;
end;
function TTestCase.Derived1Specific(Arg1: Integer): Integer;
begin
Result := Arg1;
end;
function TTestCase.Derived2_Base1(const Arg1: string; const Arg2: Double): Boolean;
begin
Result := True;
writeln('2:',arg1,arg2);
inc(cnt);
end;
function TTestCase.Derived2_Base2(const Arg1: TDateTime; const Arg2: Single): Boolean;
begin
Result := True;
end;
function TTestCase.Derived2_Base3(const Arg1: WideString; const Arg2: Integer): Boolean;
begin
Result := True;
end;
function TTestCase.Derived2Specific(Arg1: Integer): Integer;
begin
Result := Arg1;
end;
function TTestCase.Derived1: IDerived1;
begin
Result := Self;
end;
function TTestCase.Derived2: IDerived2;
begin
Result := Self;
end;
var
TestCase: ITestCase;
begin
TestCase := TTestCase.Create;
TestCase.Derived1.Base1('called from derived1', 3.14159);
TestCase.Derived2.Base1('called from derived2', 2.7178);
if cnt<>2 then
halt(1);
end.
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