Свойства, события и делегаты методов

// Проследите фактическое поведение PropertyDemo.
program PropertyDemo;
{$APPTYPE CONSOLE}
type
  TCounter = class
  private
    FValue: Integer;
  public
    property Value: Integer read FValue;
    procedure Increment;
  end;
procedure TCounter.Increment;
begin Inc(FValue); end;
var
  C: TCounter;
begin
  C := TCounter.Create;
  try
    C.Increment;
    Writeln(C.Value);
  finally C.Free; end;
end.

// Определите реальную гарантию в EventLifetime.
program EventLifetime;
{$APPTYPE CONSOLE}
type
  TNotify = procedure(Sender: TObject) of object;
  TSource = class
    OnDone: TNotify;
    procedure Finish;
  end;
  TReceiver = class
    procedure Handle(Sender: TObject);
  end;
procedure TSource.Finish;
begin
  if Assigned(OnDone) then
    OnDone(Self);
end;
procedure TReceiver.Handle(Sender: TObject);
begin Writeln('done'); end;
var
  Source: TSource;
  Receiver: TReceiver;
begin
  Source := TSource.Create;
  Receiver := TReceiver.Create;
  Source.OnDone := Receiver.Handle;
  Receiver.Free;
  try
    Source.Finish;
  finally
    Source.Free;
  end;
end.

// Отделите правило языка от удачного запуска EventReplacement.
program EventReplacement;
{$APPTYPE CONSOLE}
type
  TNotify = procedure(Sender: TObject) of object;
  TSource = class
  public
    OnChange: TNotify;
    procedure Change;
  end;
  TReceiver = class
  public
    Name: string;
    procedure Handle(Sender: TObject);
  end;
procedure TSource.Change;
begin if Assigned(OnChange) then OnChange(Self); end;
procedure TReceiver.Handle(Sender: TObject);
begin Writeln(Name); end;
var
  Source: TSource;
  First, Second: TReceiver;
begin
  Source := TSource.Create;
  First := TReceiver.Create;
  Second := TReceiver.Create;
  try
    First.Name := 'first';
    Second.Name := 'second';
    Source.OnChange := First.Handle;
    Source.OnChange := Second.Handle;
    Source.Change;
  finally
    Source.Free;
    First.Free;
    Second.Free;
  end;
end.

// Определите реальную гарантию в MethodPointer.
program MethodPointer;
{$APPTYPE CONSOLE}
type
  TNotify = procedure(Sender: TObject) of object;
  TReceiver = class
    procedure Handle(Sender: TObject);
  end;
procedure TReceiver.Handle(Sender: TObject);
begin Writeln(Sender.ClassName); end;
var
  R: TReceiver;
  H: TNotify;
  Sender: TObject;
begin
  Sender := TObject.Create;
  try
    R := TReceiver.Create;
    H := R.Handle;
    R.Free;
    H(Sender);
  finally
    Sender.Free;
  end;
end.

// Setter проверяет инвариант до изменения поля.
program SetterInvariant;
{$APPTYPE CONSOLE}
uses System.SysUtils;
type
  TAccount = class
  private
    FLimit: Integer;
    procedure SetLimit(const Value: Integer);
  public
    property Limit: Integer read FLimit write SetLimit;
  end;
procedure TAccount.SetLimit(const Value: Integer);
begin
  if Value < 0 then
    raise EArgumentOutOfRangeException.Create('Limit');
  FLimit := Value;
end;
var
  Account: TAccount;
begin
  Account := TAccount.Create;
  try
    Account.Limit := 10;
    try
      Account.Limit := -1;
    except
      on E: EArgumentOutOfRangeException do
        Writeln(E.ClassName);
    end;
    Writeln(Account.Limit);
  finally
    Account.Free;
  end;
end.