Generic singleton

Patterns.Singleton.Generic.Example.pas

uses Patterns.Singleton.Generic;
  
var o1, o2: TSingleton<TStringList>;
    s1, s2, s3: string;
begin
  o1.Get.AddStrings(['a1', 'a2']);
  s1 := o1.Get.Text;  // return "a1<cr,lf>a2"
  s2 := o2.Get.Text;  // return "a1<cr,lf>a2"
  s3 := TSingleton<TStringList>.Get.Text;  // // return "a1<cr,lf>a2"

  // Dispose the TStringList singleton
  TSingleton<TStringList>.Dispose;
end.

Patterns.Singleton.Generic.pas

unit Patterns.Singleton.Generic;

interface

type
  TSingleton<T: class, constructor> = class abstract
  strict private
    class var FInstance: T;
  public
    class function Get: T;
    class procedure Dispose;
  end;

implementation

class function TSingleton<T>.Get: T;
begin
  if not Assigned(FInstance) then
    FInstance := T.Create;
  Result := FInstance;
end;

class procedure TSingleton<T>.Dispose;
begin
  if Assigned(Self.FInstance) then begin
    FInstance.Free;
    FInstance := nil;
  end;
end;

end.