Delphi concept

Delphi/fixtures/App.dpr

@@ -0,0 +1,19 @@
+program App;
+
+{$APPTYPE CONSOLE}
+
+uses
+  System.SysUtils,
+  UAuth in 'UAuth.pas';
+
+var
+  Svc: TAuthService;
+
+begin
+  Svc := TAuthService.Create;
+  try
+    Writeln(Svc.Login('olaf', 'secret'));
+  finally
+    Svc.Free;
+  end;
+end.

Delphi/fixtures/UAuth.pas

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+unit UAuth;
+
+interface
+
+uses
+  System.SysUtils,
+  System.Classes;
+
+type
+  ITokenValidator = interface
+    ['{11111111-1111-1111-1111-111111111111}']
+    function Validate(const AToken: string): Boolean;
+  end;
+
+  TAuthService = class(TInterfacedObject, ITokenValidator)
+  public
+    function Validate(const AToken: string): Boolean;
+    function Login(const AUser, APass: string): string;
+  end;
+
+implementation
+
+function TAuthService.Validate(const AToken: string): Boolean;
+begin
+  Result := AToken <> '';
+end;
+
+function TAuthService.Login(const AUser, APass: string): string;
+begin
+  if Validate(AUser + ':' + APass) then
+    Result := 'ok'
+  else
+    Result := '';
+end;
+
+end.