Jirka Pudil se s námi podělil o to, jak zůstat v suchu i když management neustále vymýšlí nové způsoby, jak to zkomplikovat.

1. Keep yourself DRY
How not to repeat yourself
☔
but not 💩 up abstraction

2. Jiří Pudil
from Brno, CZE
open-sourcerer
coffee addict
guitar noisemaker

3. DRY
☔
Don't Repeat Yourself

4. Don't Repeat Yourself
Every piece of knowledge must have a single, unambiguous,
authoritative representation within a system
“

5. Don't Repeat Yourself
A modification of any single element of a system does not require
a change in other logically unrelated elements.
“

6. Let's write some <code/>

7. 📝 👉 📧

8. We're sending a weekly digest to users by cron
class SendWeeklyDigestCommand extends Command
{
public function execute($input, $output): int
{
// …
foreach ($users as $user) {
mail(
$user->email,
'Weekly Digest',
$weeklyDigestBody,
['From' => $this->systemEmail]
);
}
return self::SUCCESS;
}
}

9. 󰳖
We want to send the last week's digest upon registration.

10. 󰳕
OK.

11. 🤔
I already have the mail sending code in the command.

12. 󰳕
"How do I call this CLI command from the UI controller?"

13. 󰳓
Move the domain logic into a separate layer.
Call it from both places.

14. class WeeklyDigestSender
{
public function __construct(private readonly string $systemEmail) {}
public function send(User $user): void
{
// …
mail(
$user->email,
'Weekly Digest',
$weeklyDigestBody,
['From' => $this->systemEmail]
);
}
}

15. class SendWeeklyDigestCommand extends Command
{
public function execute($input, $output): int
{
// …
foreach ($users as $user) {
$this->weeklyDigestSender->send($user);
}
return self::SUCCESS;
}
}

16. class UserRegistrationController extends Controller
{
public function actionRegister($formData): void
{
// …
$this->weeklyDigestSender->send($user);
$this->redirectTo('Homepage');
}
}

17. Domain
Logic
UI controller
CLI command
API handler

18. 󰳖
People forget passwords. We need to allow them
to reset their password.

19. 󰳕
OK.

20. 🤔
I already have the mail sending code in the domain layer.

21. class WeeklyDigestSender
{
public function __construct(private readonly string $systemEmail) {}
public function send(User $user): void
{
// …
mail(
$user->email,
'Weekly Digest',
$weeklyDigestBody,
['From' => $this->systemEmail]
);
}
}

22. 󰳓
OOP blah blah abstraction blah blah inheritance!

23. abstract class EmailSender
{
public function __construct(private readonly string $systemEmail) {}
public function send(User $user): void
{
mail(
$user->email,
$this->getSubject(),
$this->getBody(),
['From' => $this->systemEmail]
);
}
abstract protected function getSubject(): string;
abstract protected function getBody(): string;
}

24. class WeeklyDigestSender extends EmailSender
{
protected function getSubject(): string
{
return 'Weekly Digest';
}
protected function getBody(): string
{
// …
return $weeklyDigestBody;
}
}

25. class PasswordResetSender extends EmailSender
{
protected function getSubject(): string
{
return 'Reset your password';
}
protected function getBody(): string
{
// …
return $passwordResetBody;
}
}

26. 🤦

27. 󰳕
Huh, there's a bug somewhere.

28. class PasswordResetSender extends EmailSender
{
protected function getSubject(): string
{
return 'Reset your password';
}
protected function getBody(): string
{
// …
return $passwordResetBody;
}
}

29. abstract class EmailSender
{
public function send(User $user): void
{
mail($user->email, $this->getSubject(), $this->getBody());
}
abstract protected function getSubject(): string;
abstract protected function getBody(): string;
}

30. class PasswordResetSender extends EmailSender
{
protected function getSubject(): string
{
return 'Reset your password';
}
protected function getBody(): string
{
// …
return $passwordResetBody;
}
}

31. 󰳕
Huh, I need some user data in the password reset email.

32. class PasswordResetSender extends EmailSender
{
protected function getSubject(): string
{
return 'Reset your password';
}
protected function getBody(User $user): string
{
// …
return $passwordResetBody;
}
}

33. abstract class EmailSender
{
public function send(User $user): void
{
mail(
$user->email,
$this->getSubject(),
$this->getBody($user),
);
}
abstract protected function getSubject(): string;
abstract protected function getBody(User $user): string;
}

34. class WeeklyDigestSender extends EmailSender
{
protected function getSubject(): string
{
return 'Weekly Digest';
}
protected function getBody(User $user): string
{
// …
return $weeklyDigestBody;
}
}

35. class WeeklyDigestSender extends EmailSender
{
protected function getSubject(): string
{
return 'Weekly Digest';
}
protected function getBody(User $user): string
{
// … I don't really need $user :/
return $weeklyDigestBody;
}
}

36. Don't Repeat Yourself
A modification of any single element of a system does not require
a change in other logically unrelated elements.
“

37. 󰳕
Huh, I need some other data in the password reset email.

38. class PasswordResetSender extends EmailSender
{
public function __construct(
private readonly DataProvider $provider,
) {}
// …
}

39. class PasswordResetSender extends EmailSender
{
public function __construct(
private readonly DataProvider $provider,
) {
parent::__construct();
}
// …
}

40. class PasswordResetSender extends EmailSender
{
public function __construct(
private readonly DataProvider $provider,
string $systemEmail,
) {
parent::__construct($systemEmail);
}
// …
}

41. 🤯
This is hell!

42. 🤯
This is constructor hell!

43. 🤔
Also, how do I test this code?

44. class WeeklyDigestSender
{
public function __construct(private readonly string $systemEmail) {}
public function send(User $user): void
{
// …
mail(
$user->email,
'Weekly Digest',
$weeklyDigestBody,
['From' => $this->systemEmail]
);
}
}

45. 󰳓
blah blah ahem composition?

46. class EmailSender
{
public function __construct(private readonly string $systemEmail) {}
public function send(
User $user,
string $subject,
string $body,
): void
{
// …
mail($user->email, $subject, $body, ['From' => $this->systemEmail]);
}
}

47. class WeeklyDigestSender
{
public function __construct(private readonly EmailSender $sender) {}
public function send(User $user): void
{
// …
$this->sender->send(
$user,
'Weekly Digest',
$weeklyDigestBody,
);
}
}

48. class PasswordResetSender
{
public function __construct(private readonly EmailSender $sender) {}
public function send(User $user): void
{
// …
$this->sender->send(
$user,
'Reset your password',
$passwordResetBody,
);
}
}

49. class PasswordResetSender
{
public function __construct(private readonly EmailSender $sender) {}
public function send(User $user): void
{
// …
$this->sender->send(
$user,
'Reset your password',
$passwordResetBody,
);
}
}

50. class PasswordResetSender
{
public function __construct(private readonly EmailSender $sender) {}
public function send(User $user): void
{
// …
$this->sender->send(
$user,
'Reset your password',
$passwordResetBody,
);
}
}

51. class PasswordResetSender
{
public function __construct(
private readonly EmailSender $sender,
private readonly DataProvider $provider,
) {}
public function send(User $user): void
{
// …
$this->sender->send(
$user,
'Reset your password',
$passwordResetBody,
);
}
}

52. 👤

53. 󰳕

54. 󰳖

55. 󰳖
People will read emails on bricks these days.
Password reset must include plain-text format.

56. class EmailSender
{
public function send(
User $user,
string $subject,
string $body,
string|null $plainTextBody = null,
): void
{
// …
$body = $this->combineBodies($body, $plainTextBody);
// …
}
}

57. 󰳖
We need to add a List-Unsubscribe header
to the weekly digest.

58. class EmailSender
{
public function send(
User $user,
string $subject,
string $body,
string|null $plainTextBody = null,
string|null $unsubscribeLink = null,
): void
{
// …
$headers = ['From' => $this->systemEmail];
if ($unsubscribeLink !== null) {
$headers['List-Unsubscribe'] = $unsubscribeLink;
}
// …
}
}

59. 󰳖
Oh, and we want to send weekly digests
from a different email address…

60. class EmailSender
{
public function send(
User $user,
string $subject,
string $body,
string|null $plainTextBody = null,
string|null $unsubscribeLink = null,
string|null $from = null,
): void
{
// …
$headers = ['From' => $from ?? $this->systemEmail];
// …
}
}

61. 󰳖
We want to log emails in dev environment
instead of actually sending them.

62. class EmailSender
{
public function __construct(private readonly string $systemEmail, private readonly bool $isDev)
public function send(
User $user,
string $subject,
string $body,
string|null $plainTextBody = null,
string|null $unsubscribeLink = null,
string|null $from = null,
): void
{
// …
if ($this->isDev) { /* … */ } else { /* … */ }
}
}

63. 󰳕
Hm, I just want to store the emails in an array
in tests.

64. class EmailSender
{
private array $sentEmails = [];
public function send(
User $user,
string $subject,
string $body,
string|null $plainTextBody = null,
string|null $unsubscribeLink = null,
string|null $from = null,
): void
{
// …
$this->sentEmails[] = /* … */;
}
}

65. 󰳖
It's time we added email verification.

66. class EmailVerificationSender
{
public function __construct(private readonly EmailSender
$sender) {}
public function send(User $user): void
{
$this->sender->send();
}
}

67. 😱

68. 󰳕
"How do I call this CLI command from the UI controller?"

70. 󰳓
Always question your abstractions
in the face of requirement changes.

71. 🛌

72. ☕

73. 👀

74. class Message
{
public function setFrom(string $from): void { /* … */ }
public function setTo(string $to): void { /* … */ }
public function setSubject(string $subject): void { /* … */ }
public function setBody(string $htmlBody): void { /* … */ }
// …
}

75. interface Transport
{
public function send(Message $message): void;
}

76. class EmailVerificationSender
{
public function __construct(
private readonly Transport $transport
) {}
public function send(User $user): void
{
$message = new Message();
// …
$this->transport->send($message);
}
}

77. class PasswordResetSender
{
public function __construct(
private readonly Transport $transport
) {}
public function send(User $user): void
{
$message = new Message();
// …
$this->transport->send($message);
}
}

78. class WeeklyDigestSender
{
public function __construct(
private readonly Transport $transport
) {}
public function send(User $user): void
{
$message = new Message();
// …
$this->transport->send($message);
}
}

79. class WeeklyDigestSender
{
public function __construct(
private readonly Transport $transport
) {}
public function send(User $user): void
{
$message = new Message();
// …
$this->transport->send($message);
}
}

80. Don't Repeat Yourself
Every piece of knowledge must have a single, unambiguous,
authoritative representation within a system
“

81. Don't Repeat Yourself
Every piece of knowledge must have a single, unambiguous,
authoritative representation within a system
“

82. class WeeklyDigestSender
{
public function __construct(
private readonly Transport $transport
) {}
public function send(User $user): void
{
$message = new Message();
// …
$this->transport->send($message);
}
}

83. production:
transport: SmtpTransport(…)

84. production:
transport: SmtpTransport(…)
development:
transport: FileLoggingTransport

85. DRY
☔

86. 󰳖
So, we were talking with other managers, and …

87. Jiří Pudil
@jiripudil
me@jiripudil.cz
https://jiripudil.cz

88. 󰳓
Always question your abstractions
in the face of requirement changes.