IntfMethodResolution.pas

  IFoo = interface
    ['{4061C455-B122-48D6-940F-9C1B2FD4A689}']
  end;

  IDoesntWorkFactory = interface
    ['{E9A093ED-C429-46C3-82DD-D5D32EB9120F}']
    function Create(const Blabla: string): IFoo; overload;
    function Create(const Blabla: Integer): IFoo; overload;
  end;

  IWorkingFactory = interface
    ['{E32C2F49-F6E4-4D7F-B1DF-787C3CC55A39}']
    function Create(const Blabla: string): IFoo;
  end;

  TWorkingFactoryImpl = class(TInterfacedObject, IWorkingFactory)
  strict private
    function IWorkingFactory.Create = FooCreate;
    function FooCreate(const Blabla: string): IFoo;
  end;

  TDoesntWorkFactoryImpl = class(TInterfacedObject, IDoesntWorkFactory)
  strict private
    function IDoesntWorkFactory.Create = FooCreate;
    function IDoesntWorkFactory.Create = FooCreate; // identifier redeclared
    function FooCreate(const Blabla: string): IFoo; overload;
    function FooCreate(const Blabla: Integer): IFoo; overload;
  end;

This doesn't work aswel:

  TDoesntWorkFactoryImpl = class(TInterfacedObject, IDoesntWorkFactory)
  strict private
    function IDoesntWorkFactory.Create = FooCreateString;
    function IDoesntWorkFactory.Create = FooCreateInteger; // identifier redeclared
    function FooCreateString(const Blabla: string): IFoo;
    function FooCreateInteger(const Blabla: Integer): IFoo;
  end;

"Not so ideal" method name 'Create' isn't the problem either

  IDoesntWorkFactory = interface
    ['{E9A093ED-C429-46C3-82DD-D5D32EB9120F}']
    function DoIt(const Blabla: string): IFoo; overload;
    function DoIt(const Blabla: Integer): IFoo; overload;
  end;

  TDoesntWorkFactoryImpl = class(TInterfacedObject, IDoesntWorkFactory)
  strict private
    function IDoesntWorkFactory.DoIt= DoItString;
    function IDoesntWorkFactory.DoIt= DoItStringInteger; // identifier redeclared
    function DoItString(const Blabla: string): IFoo;
    function DoItStringInteger(const Blabla: Integer): IFoo;
  end;