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Modern Pascal (Object Pascal / FreePascal) supports full OOP with classes, inheritance, virtual methods, interfaces.

program demo;

type
    TPerson = class
    private
        FName: string;
        FAge: integer;
    public
        constructor Create(const AName: string; AAge: integer);
        function Greeting: string;
        property Name: string read FName write FName;
        property Age: integer read FAge write FAge;
    end;

constructor TPerson.Create(const AName: string; AAge: integer);
begin
    FName := AName;
    FAge := AAge;
end;

function TPerson.Greeting: string;
begin
    Result := 'Hi, I''m ' + FName;
end;

var
    p: TPerson;
begin
    p := TPerson.Create('Ada', 36);
    try
        WriteLn(p.Greeting);
        WriteLn(p.Name, ' is ', p.Age);
    finally
        p.Free;
    end;
end.

Key conventions:

• Class names start with T (Type)
• Field names start with F (Field) — usually private
• Use property to expose with getter/setter — clean syntax for callers
• Always Free instances in finally (manual memory)

Inheritance:

type
    TAnimal = class
    public
        function Sound: string; virtual;
    end;

    TDog = class(TAnimal)
    public
        function Sound: string; override;
    end;

function TAnimal.Sound: string;
begin
    Result := 'generic';
end;

function TDog.Sound: string;
begin
    Result := 'woof';
end;

virtual declares the parent's method as overridable. override matches it. Without virtual/override, the method is statically dispatched.

abstract methods — declared but not implemented:

TShape = class
public
    function Area: real; virtual; abstract;
end;

Must be overridden in concrete subclasses.

Visibility:

• private — within unit
• protected — descendants
• public — anyone
• published — public + RTTI for runtime introspection (Delphi heritage)